On a misty February morning midway between Britain and France, we watch tankers carrying Russian oil worth around $100m (£74.1m) cruise past in defiance of Western sanctions, embargoes, and price caps.

Dozens of these vessels pass through the Channel every month, part of a "shadow fleet" of up to 800 vessels that have kept the oil revenues that fund the war on Ukraine flowing.

This week, the UK government announced fresh sanctions against the Russian oil trade but the evidence of a day on the water is that the shadow fleet operates with apparent impunity, right under the nose of Kyiv's allies.

Russian tankers a 'routine sight'

Our skipper, Matt Coker, usually takes sea fishing parties out on the Portia, but we were after a bigger catch; three vessels in the shadow fleet carrying oil from Russia's Baltic ports.

He says they are a routine sight in the world's busiest shipping lane: "When you see these Russian ships and these oil tankers, you know, it's a regular occurrence. To be honest, no one really takes any notice."

We had tracked the tankers - the Rigel, the Hyperion and the Kousai - from the Gulf of Finland, where they had been loaded with oil at Russian Baltic ports, to intercept them as they passed the narrowest point of the Dover Straits.

Up close in a rising swell, the scale of the vessels is unavoidable, and each one tells a story about both the impact and the limits of Western action.

The Rigel, a Suezmax-class tanker, is more than 270 metres long and fills the near horizon as it emerges from the mist. With a capacity of one million barrels, its cargo of oil, loaded a week earlier at Primorsk, is worth around $55m (£40.7m).

It is sailing under a Cameroon flag, owned and managed by a company in the Seychelles, and sanctioned by the EU, UK and Canada, among others.

That prevents it from using port facilities in any of the sanctioning countries, but not from heading to its next known stop, Port Said at the head of the Suez Canal. We cannot know where its oil will be unloaded, but since the invasion of Ukraine, the bulk of Russian oil has been sold to China and India, at a significant discount.

Next to appear is the Hyperion, sanctioned by the UK, EU and US, and sailing under a Russian flag with its name marked on the bow in Cyrillic.

The flag switching tactic

As recently as December, it was sailing under a Sierra Leone flag when, after making a delivery to Venezuela, it switched flags and evaded the US naval blockade in the Caribbean.

Switching flags is a routine tactic in the shadow fleet, opaque ownership is common, and insurance cover is often unclear, a serious concern given many of the vessels are ageing and poorly maintained.

The US has taken direct military action against tankers in the shadow fleet linked to Venezuela, with at least seven seized since last year, the most recently in the Indian Ocean on Tuesday.

French paramilitaries also seized a vessel in the Mediterranean last month, but despite the almost daily passage of shadow tankers through the Channel, direct British interventions so far have focused on insurance.

As we watch the passage of our third sanctioned tanker, the Kousai, we overhear a message from the coastguard to its captain on the open VHF radio channel, demanding proof of insurance.

The captain is asked to email documentation to a government email address within 24 hours. We do not hear the Kousai's response, and in a matter of minutes, it too has passed.

A reaction to sanctions

Sanctions against Russia's oil industry have had an impact, reducing the value of Russian oil if not the volumes that it moves.

The growth of the shadow fleet itself is a market response to tightening sanctions. With the majority of western-controlled tankers and associated marine services beyond Russia's reach, it turned to an ad-hoc, opaque collection of older vessels to move oil, often covertly.

"Over 60% of Russian crude is being exported on the shadow fleet," says Pamela Munger, head of European market analysis for energy analysts Vortexa.

"You have more vessels that need to be in the chain. Let's say a sanctioned vessel loads Russian crude and let's say it's on its way to China.

"It could make up to five, six, seven ship-to-ship transfers along the way in order to disguise the origin of the crude and move it on to… Non-sanctioned vessels, which it will eventually discharge into its end buyer."

Data from the Centre for Research on Energy and Clean Air shows that the number of vessels in the shadow fleet grew following sanctions but the volume of oil being moved remained constant, even as hundreds of vessels were sanctioned directly.

Impact on the oil market

Prices have fallen, however, with Russian oil now competing with Iranian and Venezuelan crude in the "distressed" sanctioned oil market, cutting Kremlin revenues as a result.

"Russia has had to discount those crude oil cargoes in a very big way," says David Fyfe, chief economist at commodity price specialists Argus Media.

"In 2021, Urals, the primary export grade of Russian crude, was pricing two to three dollars below North Sea Brent. As we speak in February, Urals is loading in the Baltic ports at $27 below North Sea Brent."

That price gap has cut Russia's oil revenues by around 25% year-on-year and by up to 50% in January alone, an economic impact the Kremlin cannot ignore.

"I think they'll take a fairly sizeable hit, particularly in revenues this year, and I'd expect, at the very least, something like a half-a-million barrel per day hit on volumes," says Mr Fyfe.

Are we heading for a military confrontation?

The squeeze could tighten further, with pressure for a more robust response from European nations, including the UK.

Under maritime law, all vessels have the right of innocent passage as long as they are sailing under a legitimate flag, and many countries have continued to do business with Russia since the invasion of Ukraine.

The UK government is understood to have examined the legal grounds for detaining Russian tankers, including under the Sanctions and Money Laundering Act.

"I think there must come a point at which Britain and its allies, the Dutch, and the Danes and the Norwegians and the seagoing nations of Northern Europe, they will get much tougher with these Russian ships, even if they're escorted," says Professor Michael Clarke, Sky News security and defence analyst.

"When that happens, I think we're heading probably sometime this year for some sort of militarised confrontation at sea."

A Ministry of Defence spokesperson said it has requested insurance documents from more than 600 vessels, and that "deterring, disrupting and degrading the Russian shadow fleet is a priority".

The owners of the Rigel, the Hyperion and the Kousai have been contacted for comment.

There is a massive amount of American firepower now in the region, and its commander-in-chief has issued Tehran with multiple warnings: Make a deal or else.

But what if they don't?

The president's plan appears to have been to use the US Navy to force the Iranians to accept his terms with a gun to their head, but it's not working out.

His chief negotiator, Steve Witkoff, has admitted as much.

"He's curious", he said of Trump, "as to why they haven't capitulated, why under this sort of pressure with the amount of naval power that we have over there, why they haven't come to us."

So what now? The president "understands that he's got plenty of alternatives", claims Witkoff, but does he?

Option one

One option could be calibrated strikes. Whack Iran once and see if that makes its government more amenable.

Experts say that could prove a massive miscalculation. The Iranian government is in a tight spot, no doubt, but it may try to ride out the storm if it's just a series of strikes.

Option two

Or the president could authorise attacking Iran with full force. But that's problematic too.

Observers warn that for all the military muscle mustered in the region, there is still not enough to sustain an extended air campaign.

In leaks infuriating the president, his own commanders at the Pentagon have been warning as much.

Two carrier strike groups and all the warplanes sent to bases to bolster them could bombard Iran for a week, at most two, it is thought.

That would be painful for the Iranians, but they could try to hunker down and tough that out, too. And they would strike back with their formidable arsenal of ballistic missiles.

Option three

Attacking Iran comes with considerable jeopardy for the president. But so does walking away.

For all his bellicose rhetoric, the "TACO president"i could chicken out and send his aircraft carriers back to base.

Read more from Sky News:
How Iran may be preparing for US strike
Is Tehran ready to strike a deal?

But having built up so much firepower, doing nothing would look weak and have consequences: for America's standing and the president's own political fortunes at a time when his approval ratings are cratering.

Talks in Geneva scheduled for Thursday offer an off-ramp. Iran has another chance to "capitulate", as Witkoff puts it. But they are past masters at brinkmanship and calling their enemies' bluff.

If they do so, has the US president thought this all through, or has he cooked his own goose?

Thames Valley Police (TVP) began searches of Royal Lodge in Windsor Great Park, Berkshire, following the arrest of the former prince at Sandringham on what was his 66th birthday last Thursday.

Andrew was released under investigation after spending 11 hours in custody on suspicion he shared sensitive information with late sex offender Jeffrey Epstein when he served as UK trade envoy between 2001 and 2011.

He has always vigorously denied any allegations of wrongdoing in connection with Epstein.

Read more from Sky News:
What is misconduct in public office?

TVP assistant chief constable Oliver Wright said: "Officers have now left the location we have been searching in Berkshire. This concludes the search activity that commenced following our arrest of a man in his sixties from Norfolk on Thursday.

"We understand the significant public interest in this case and our investigation remains ongoing.

"It is important that our investigators are given the time and space to progress their work. We will provide updates when it is appropriate to do so, but this is unlikely to be for some time."

'Rude, arrogant and entitled'

It comes after MPs officially backed the release of files relating to Andrew's appointment as UK trade envoy.

On Tuesday, MPs unanimously agreed on the release without needing for it to go to a vote.

Trade minister Sir Chris Bryant insisted the government would release the files "as soon as is practicable and possible within the law" but said that any documents relating to the offence of misconduct in public office may be held back on the advice of prosecutors.

In a critique of Andrew, he called the former Duke of York "rude, arrogant and entitled" and described him as "a man on a constant self-aggrandising and self-enriching hustle".

Sir Chris spoke of his own experience of Andrew visiting his constituency, claiming the King's brother had insisted on travelling to an event there via helicopter, "unlike his mother [Queen Elizabeth II], who came twice to the Rhondda and always came by car".

"That is, of course, Mr Speaker, not a crime, nor is arrogance," he added.

Earlier this week, the governments of Australia and New Zealand backed plans to remove Andrew from the royal line of succession.

Changing the line of succession would require the agreement of all 15 realms of the Commonwealth where the British monarch is also the head of state.

Only New Zealand and Australia have so far backed the move.

European prime ministers and dignitaries had come to Maidan Square in Kyiv as an act of solidarity and remembrance as they set candles in front of the sea of crosses, photos, and flags that now adorn this makeshift memorial for those killed in this conflict.

But equally, there is an acknowledgement from those gathered that when it comes to this war, there is no end in sight: the leaders who arrived in Ukraine to mark this anniversary expect to be coming back next year, too.

For Yvette Cooper, the foreign secretary, the trip was a moment to focus not just on sanctions, weapon supplies and territory, but to try to highlight the war Vladimir Putin is waging against women and children in Ukraine as he wages a "war on Ukrainian culture".

"I think one of the things that's been clearly happening, the way that so many children have been stolen, the ways in which, in the temporarily occupied territories, they are trying to change the education system, trying to choke out the Ukrainian language," she said.

"It's an attempt really, not just about territory, but to have a war on Ukrainian families, to have war on Ukraine history and culture and identity."

But even as she arrived in Ukraine, issues at home plaguing the government and her foreign office brief were dominating the agenda, with the former US ambassador that she sacked, Peter Mandelson, arrested and taken in for hours of questioning by the police as Ms Cooper took an overnight train to Ukraine.

The foreign secretary, who sacked the ambassador just days into her job in September, reiterated her position that Lord Mandelson "should never have been appointed" and, in a rare flash of emotion, told me that "vile" emails were exchanged between Lord Mandelson and paedophile financier Jeffrey Epstein.

In one of the emails released by the US Department of Justice, Epstein replies to Lord Mandelson asking how being free from jail felt, by saying "she feels fresh, firm and creamy". Lord Mandelson replied by calling Epstein a "naughty boy".

"That's just vile," she told me. "It makes me feel so angry."

"I've been really clear, Peter Mandelson should never have been appointed as ambassador to the US and I think some of what has been so, so deeply frustrating about all of this is that really at the heart of all of these should be the victims of Epstein, they're women and children who faced the most horrendous criminal exploitation trafficking and that really should be the focus.

"As you know, when I was home secretary, I made it a mission for the government to halve violence against women and girls over the next 10 years.

"That's a strategy now that the prime minister has championed. And now, as foreign secretary, I am making tackling violence against women and girls something that is an international theme for us as well."

Putin's 'genocidal intent'

On that issue, Ms Cooper used her time in Ukraine to meet female victims of Russian aggression and sexual violence and the "voices for children" charity with Olena Zelenska to highlight the plight of thousands of children stolen from their Ukrainian families by Russia.

Yevgen Zakharov, a civil rights activist working at the Civil Liberties Centre, told the foreign secretary on her visit there that Putin "wants to eliminate Ukrainian identity".

"This is his crazy idea, a genocidal intent is there," he said.

Throughout these visits, we heard stories of women in Russian-occupied territory being beaten, sexually abused, falsely imprisoned and sent to Labour camps.

Elena Jagapova spoke of how she was taped to a chair, beaten until bloodied, sexually abused and sent to a labour camp. Another, Julia, told us of how her children - then 10 and 17 - were abducted by the Russians, and her 19-month battle to get them back.

Ms Zelenska says more than 20,000 Ukrainian children have been stolen by the Russians as part of their campaign to eradicate Ukrainian culture, through repressing the language, forcing indoctrination and trying to brainwash children.

"We heard stories not just of torture, but also of this attempt to really destroy Ukrainian culture and identity as well," said Ms Cooper.

"That's why it's so important that we provide support for Ukrainian families, support for Ukrainian services but, also, make sure that you could have the kind of special tribunal, the kind of court processes, international court processes, that can pursue exactly those questions and can make sure that there is some justice and accountability."

No end in sight…

The UK has made it clear to Ukraine that it will play a part in helping set up war crime courts when this conflict finally ends, in echoes of Britain's role in the Nuremberg trials that punctuated the Second World War.

But when that moment comes is hard to see. Those who gathered in Ukraine on Tuesday did so with a weariness that has come to characterise an attritional war in which Russia isn't winning, but neither is it defeated, as Europe and the US give enough support for Ukraine to fight on, without the firepower - or sanctions against Russia - for it to truly succeed.

Mr Zelenskyy warned on the eve of the fourth anniversary that Putin had already started World War Three and Ukraine was the outpost, the frontline pushing Putin back.

Ms Cooper doesn't want to use that language, but she does acknowledge that Russian aggression is here to stay, and allies must support Ukraine for however long it takes.

To that end, the UK introduced another sanctions package on Tuesday, and is pushing the US and Europe about a maritime services ban to make it much harder for Russia's shadow fleet to transport Russian oil.

The frustration is that the US, in trying to pursue peace talks - and reportedly in favour of Russian demand that Ukraine cede the 20% of the Donbas territory not under Russian occupation as part of any truce, is reluctant to squeeze Russia economically right now.

…but a glimmer of hope

So this war grinds on. For the Ukrainians and allies, one glimmer of hope is that Russia is now losing more men that it can mobilise on the battlefield.

Ukraine hopes that if it can increase the casualty rate to 50,000 Russians a month, then Putin might be forced to consider conscription, which could prove politically difficult and begin to stall his momentum.

That Russia has sacrificed an estimated 500,000 lives in order to gain less than one per cent of Ukraine's territory tells of the attritional war in which these two sides are locked - and with the horrific loss of life.

In the meantime, Britain and Europe will try to put more pressure on the US to bring in more aggressive sanctions against Russia, to financially starve Putin's war machine.

But for all the signs of solidarity on Tuesday, there is little to show in the way of concrete steps to peace. Ukraine hopes for a game changer in the coming months, but is reconciled to more anniversaries like today.

The former Labour peer was detained on Monday under suspicion of misconduct in public office, and released later the same evening.

Sky News understands the Metropolitan Police arrested him because they had been told he was preparing to flee the UK for the British Virgin Islands.

They had originally planned to interview Mandelson, 72, under caution, without arrest in a fortnight's time. It is understood that going through devices obtained from searching his two homes in Camden, north London, and Wiltshire, was proving very time-consuming.

But after police conducted a series of interviews about the flight risk claims they decided they needed to arrest him this week.

Mandelson has denied any wrongdoing.

Mishcon de Rey, lawyers for the former British ambassador to the US, said: "Peter Mandelson was arrested yesterday despite an agreement with the police that he would attend an interview next month on a voluntary basis.

"The arrest was prompted by a baseless suggestion that he was planning to leave the country and take up permanent residence abroad.

"There is absolutely no truth whatsoever in any such suggestion.

"We have asked the MPS for the evidence relied upon to justify the arrest. Peter Mandelson's overriding priority is to cooperate with the police investigation, as he has done throughout this process, and to clear his name."

Lord Mandelson was bailed in the early hours of Tuesday morning after about eight hours of questioning.

It is not clear if he had to surrender his passport, but that is usually a condition of bail in such cases.

Read more: Mandelson's 'vile' Epstein emails make me 'angry', foreign sec says

He was sacked as ambassador in September after details emerged about his continued contact with disgraced paedophile Jeffrey Epstein.

Mandelson then resigned from the House of Lords in early February amid growing public and political scrutiny after the US Department of Justice's latest publication of Epstein files last month.