Speaking to the media for the first time since Qatar has come under repeated missile and drone attacks, the prime minister told Sky News that the country had entered what he called "a very difficult period" - but praised the professionalism of its defence and security forces.
For a man who has mediated some of the world's most complex crises, what stood out to me was how angry he was about Iran's actions.
"It is a big sense of betrayal," he told me. "Just an hour after the start of the war, Qatar and other Gulf countries have been attacked. We made clear that we were not going to take part in any wars against our neighbours."
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For a country that has long kept diplomatic channels open with Tehran - even during the most volatile moments - the tone was striking.
Qatar has traditionally positioned itself as a global mediator, able to speak to everyone. That relationship with Tehran now appears strained.
"All the attacks on the Gulf countries - we never expected this from our neighbour," he said. "We have always tried to preserve a good relationship with Iran, but the justifications and pretexts they are using are completely rejected."
Yet even as he condemned the strikes, the prime minister repeatedly stressed that military escalation would only deepen the crisis - and that the responsibility to step back lies with all sides.
"We continue to seek de-escalation," he said. "They are our neighbours - it's our destiny."
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His message was directed not only at Tehran. He also called on the US to reduce tensions, warning of the risk that the entire region slides into war.
Diplomacy, he argued, remains the only viable path out of the crisis.
"The miscalculation by the Iranians to attack Gulf countries has destroyed everything," he said, but insisted the answer now must be renewed negotiations.
He also pushed back against claims that Iran's strikes were aimed at military targets.
International airports, water utilities and gas infrastructure have all been in Tehran's crosshairs.
The prime minister added: "25% of the attacks are targeting civilian facilities. What has this got to do with the war? What do they want to achieve?"
Over and over again, he returned to the global stakes - and that what happens in the Gulf won't stay in the Gulf.
Qatar supplies roughly 20% of the world's gas and is one of the planet's largest fertiliser producers - meaning any sustained disruption would impact markets, food supplies and people worldwide.
Even as the Gulf states insist this is not their fight, however, they are an integral aspect of it.
And that, perhaps, is the central danger of this moment - a war that began between the US, Israel and Iran is now dragging in countries that want no part of it, but increasingly find themselves on its front lines.
General Sir Richard Barrons told Sky News this meant politicians would have to make "very difficult choices" to shift investment away from peacetime priorities such as health and welfare but that - following the eruption of war between the US and Israel against Iran - the world has become even more dangerous than when his review was published last June.
The Ministry of Defence has faced questions about how ready it is for conflict after failing to be able to deploy a single warship rapidly from Portsmouth to bolster the defences of two British sovereign bases in Cyprus, amid threats from Iranian missile and drone strikes.
HMS Dragon, a Type 45 destroyer - the only piece of kit in the British arsenal capable of shooting down ballistic missiles - will only depart for the eastern Mediterranean in the coming days, at least a week since Sir Keir Starmer announced the deployment.
By contrast, the Royal Navy was able to rush two aircraft carriers and multiple other warships from the UK within three days of Argentina invading the Falklands in 1982.
General Barrons said the Strategic Defence Review, which set out how to rebuild the UK's hollowed-out armed forces after decades of decline, recognised "that we live in a much more threatening world, where the risks to the UK are potentially existential".
It recommended the need to invest more in defence, while also being mindful that this would involve "some very difficult choices" about what areas of public spending would have to suffer as a result.
"The world since the review was published has just got more difficult, so the urgency is greater," the former senior military officer said.
"The government is going to have to find more money sooner ... If we don't, then we could feel like the people in Dubai and Bahrain ... and Kyiv."
Iran's retaliation to US and Israeli strikes has included waves of missiles and drones fired at neighbouring Gulf states, while Russia's full-scale invasion of Ukraine has subjected the entire country to deadly bombardments for more than four years.
"We need to do a much better job of being able to deter that [kind of threat] and see it off if it happens," General Barrons said.
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As set out in a Sky News and Tortoise podcast series called The Wargame, successive British governments took what was called a "peace dividend" after the Cold War ended in 1991, switching money out of defence and into areas such as health, welfare and the economy.
The move saw the size of the Royal Navy, army and Royal Air Force shrink significantly along with wider national resilience.
To give a sense of what has been lost, Sky News tracked the decline of the regular military from 1983 - a year after the Falklands War, when NATO allies were still maintaining large standing armed forces to face off against the then Soviet Union - and now.
In 1983, Britain had 321,000 full-time service personnel, split between 72,000 in the navy, 159,000 in the army and 90,000 in the air force.
Two decades later, long after the Cold War had ended but when the UK joined the US in invading Iraq under then Prime Minister Tony Blair, the nation had 207,000 service personnel, with 42,000 in the navy, 112,000 in the army and 53,000 in the RAF.
The latest data released by the Ministry of Defence for last year, however, show these figures now stand at 125,680 members of the full-time armed forces, comprising 27,820 in the navy, 70,300 in the army and 27,560 in the RAF.
Spending on defence as a proportion of GDP has shrunk as well, with Britain allocating 5% for the military in 1983, compared with 2.5% in 2003 and just 2.3% now.
Sir Keir has said his government will inch up defence spending to 2.5% of GDP by next year and has set an "ambition" to lift the level to 3% of GDP by the next parliament - which lasts until 2034.
However, there have been reports that he could make this move - which would cost taxpayers billions of additional pounds - by 2029, five years early.
The 56-year-old succeeds his father, Ayatollah Ali Khamenei, who was killed in his Tehran compound on the first day of the war. He was the supreme leader for more than 37 years before his death.
Mojtaba wasn't there, and so survived, but his mother, wife and daughter were killed.
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The supreme leader is chosen by the assembly of experts, a body of 88 Islamic scholars selected for their loyalty to the regime.
A building where it meets was flattened in an airstrike but none of them are thought to have been present at the time.
Little is known about Mojtaba Khamenei.
He is the second eldest son of Ayatollah Ali Khamenei and has kept a low profile over the years, rarely speaking publicly or taking Friday prayers.
The 56-year-old is a hardline conservative who served in the Habib battalion of the Islamic Revolutionary Guard Corps (IRGC) during the Iran-Iraq War in the 1980s and has been linked with the violent suppression of protests in his country.
His time in the IRGC helped him build influential connections with men who now hold senior positions in the country.
Tara Kangarlou, author of The Heartbeat of Iran, told Sky News that Mojtaba Khamenei "holds a lot of power in the IRGC apparatus; he has his hands in pretty much every infrastructure you can imagine in Iran: so a lot of money, power and influence".
Khamenei is under US sanctions but has reportedly amassed a valuable empire of properties around the world, including in London.
Unlike his father, who was a well-known intellectual, a student of Persian poetry and strong orator with a following inside Iran before he became supreme leader, Khamenei doesn't have a strong reputation in the country.
The position of supreme leader is not just the ultimate authority in Iran, he (and it's always a man) is the guardian of the Islamic Republic.
Although Khamenei studied in the holy city of Qom, he has only ever been a mid-ranking cleric, not a senior ayatollah.
By inheriting the role, the assembly of experts has in effect created a dynasty - not unlike a monarchy.
But Iranians don't like dynasties: they overthrew the Qajar dynasty in 1925 and the Pahlavi monarchy in 1979.
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Although Khamenei has influence in the inner circles of Iranian politics, he has never held public office or been elected to any government role.
In 1989, when his father became supreme leader, he worked in his offices and became his "principal gatekeeper" and "the power behind the robes", according to US diplomatic cables published by WikiLeaks.
He is close to the IRGC, and that's important because they would have been instrumental in his appointment and it suggests the hardliners retain some power - which doesn't bode well for negotiations to end the war.
A 30-year-old female suspect was taken into custody following the incident in Beverly Hills on Sunday afternoon.
Los Angeles police have said the pop star was home at the time - but it is unclear whether her partner A$AP Rocky and their three young children were inside.
It is believed that seven to nine rounds from an AR-15 rifle were fired - with four striking the house.
No injuries have been reported, with the LAPD's robbery and homicide division launching an investigation.
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Dozens of trains were cancelled on Sunday after a four-storey building in Union Street, close to Glasgow Central Station, caught fire.
The building has partially collapsed, and the station will not reopen this morning as firefighters continue to tackle the blaze - more than five hours after it began.
A spokesperson said: "Glasgow Central Station has been closed until further notice, and will not reopen on Monday morning, following a fire at a vape shop on Union Street.
"Emergency services, including Police Scotland and the Scottish Fire and Rescue Service, are on site and managing the incident.
"As a precaution, all services through Glasgow Central have been suspended, and passengers are advised to seek alternative travel arrangements.
"We will provide further updates as soon as more information becomes available."
First Minister John Swinney said in a post on X: "I am deeply concerned about the fire near Glasgow Central Station tonight, and very grateful to all of the emergency services who are responding.
"Please continue to follow travel guidance, avoid the area and stay safe."
Paul Sweeney, Labour MSP for Glasgow, said the building had partially collapsed. In a post on X, he said the building dates back to 1851.
"Sadly the building has now partially collapsed," said Mr Sweeney. "I hope the fire can be contained. The corner of the Forsyth Building, as well as the Caledonian Chambers and Central Hotel seem unaffected.
"It's a massive blow to Union Street with the restoration of the Egyptian Halls in prospect."
A Scottish Fire and Rescue Service spokesperson said: "More than 60 firefighters are currently working to tackle a large building fire on Union Street, Glasgow.
"We were alerted at 3.46pm to reports of a building fire on Union Street, Glasgow.
"At its height, nine fire appliances and specialist resources were mobilised to the area, where firefighters are currently working to extinguish a fire affecting the ground floor of a four-storey building.
"There are no reported casualties, and crews remain at the scene."
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TransPennine Express has said its services between Glasgow Central and Liverpool Lime Street and Manchester Airport will not run on Monday, and has urged passengers not to travel as there will not be any rail replacement buses.