Princess Anne laid a wreath at Wellington Arch, Hyde Park Corner, at 5am, at the event which included a reading of the John McCrae poem In Flanders Fields.
In Australia, several services were disrupted by booing from small groups during so-called Welcome to Country ceremonies, during which indigenous leaders welcome visitors to their traditional lands.
The outbursts in Melbourne, Perth, and Sydney - where one man was arrested - were also met with applause and cheering from large groups of those gathered to pay their respects, according to local media.
Later on Saturday, the Princess of Wales is due to attend a wreath-laying and parade at the Cenotaph and a service at Westminster Abbey.
The Royal Family's official account on X paid tribute with a picture of troops from the Australian and New Zealand Army Corps (ANZAC) travelling to the First World War conflict zone Gallipoli with the caption "Lest we forget".
Anzac Day is held every year on 25 April and was initially established to commemorate ANZAC troops landing on the beaches of Gallipoli in northwest Turkey in 1915. The attack on the Turkish defences began at dawn.
Ceremonies, which are marked across the world, also took place in Gallipoli and Villers-Bretonneux, a French village which Australian units helped defend during WWI.
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Booing at ceremonies
Australia's defence minister Richard Marles criticised the disruption at ceremonies, which in previous years has been perpetrated by anti-indigenous rights protesters.
"To boo in that way goes completely against that. It is deeply disgraceful," he told ABC News Breakfast.
In Sydney, police confirmed a 24-year-old man was arrested for "an alleged act of nuisance", and several others were moved on.
They represented "a small handful of people" compared to about 11,000 at the event, according to a statement from police.
Police and firefighters were called to Mason Street, south of the city centre, at about 8.30pm on Friday.
Firefighters entered the property wearing breathing equipment and rescued two young children.
Despite giving advanced life support to both children, they were pronounced dead at the scene, West Midlands Police said.
Two other children and a woman had already left the property before emergency services attended.
They were checked over by paramedics but did not require hospital treatment.
Police have erected a cordon around the scene while work is done to establish a cause for the fire. It is expected to remain in place for some time.
The house was extensively damaged in the blaze.
West Midlands Police said in a statement: "Our thoughts are with the children's loved ones and all those impacted by this heartbreaking incident."
Anyone with information has been asked to contact police.
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Steve Marston was convicted in 1998 of stealing from his branch after using the faulty accounting software called Capture.
Capture predated the infamous Horizon IT system, which saw hundreds wrongfully convicted of theft in one of the biggest miscarriages of justice in British legal history.
Mr Marston's conviction was referred by the Criminal Cases Review Commission (CCRC) to the Court of Appeal on the grounds that his prosecution amounted to an "abuse of process".
The Post Office is now requesting a two-month extension before it delivers its formal response to the case.
Last year, a Sky News investigation unearthed a long-lost document which proved that the Capture system was capable of producing "absurd gibberish".
That document is being used in Mr Marston's appeal, as well as being part of the first Capture case to be referred to the Court of Appeal - Pat Owen, who died a few years after her conviction in 1998.
Ms Owen's case was also delayed by the Post Office before Christmas last year when they applied for an extension.
Speaking to Sky News, Steve Marston said that he believed the Post Office is "determined to protect their brand at all costs despite the overwhelming proof" over faulty Capture software.
He continued: "They appear to be looking for straws in a haystack to try and discredit innocent victims rather than doing the right thing by not contesting… and accept their part in this scandal rather than trying to find a technicality to try and continue blaming postmasters."
"Shame on them," he added.
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Post Office 'regrets distress'
The government has already accepted that the Capture system was faulty, and has started paying redress to victims who were not convicted.
A Post Office spokesperson said they "acknowledge" that Mr Marston "feels frustrated" by the application and "regret the distress" caused.
They emphasised that the Post Office "wants all unsafe convictions to be overturned" and added that they will "continue to do everything we can to ensure that appeals are considered in accordance with the law and our duties to the courts."
The spokesperson also told Sky News that they need "to conduct further searches, informed by the additional information that has now been provided by the Appellant and the CCRC".
"It was acknowledged by the CCRC in their Statement of Reasons, that the referral to the Court of Appeal has been made without the benefit of access to the full case papers and evidence.
"We are working to file our Respondents Notice by the proposed new deadline."
Enzo Bettamio, 18, was put on a flight from Dubai to the UK on Friday and then formally charged with the murder of Kamonnan Thiamphanit, who was also known as Angela.
He will appear at Westminster Magistrates' Court on Saturday.
Ms Thiamphanit was found dead at her home in Stanhope Place near Hyde Park on the morning of 8 April 2024 after police forced entry to the property. She had suffered multiple stab wounds.
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Metropolitan Police Detective Chief Inspector Alison Foxwell, who is leading the investigation, said: "I would also like to express my sincere thanks to Angela's family and friends for their patience and unwavering support to the investigation, throughout what has been an incredibly difficult and distressing time for them."
The Met had referred itself to the Independent Office for Police Conduct following the murder, after officers were contacted twice by friends of Ms Thiamphanit the day before her body was discovered.
The case was graded as a medium-risk missing person inquiry before officers forced entry and discovered the 27-year-old, who had Chinese, Hong Kong and Thai nationality.
One student grabbed the steering wheel and another reached down to apply the brakes, while others called for help and gave first aid.
Bus driver Leah Taylor had 40 children on board and was on a four-lane highway when she felt an asthma attack coming.
She reached for her nebuliser but fell unconscious before she could use it.
Jackson Casnave, 12, said he noticed her head tilting back and the bus starting to swerve, so jumped up and shouted for others to help.
"I saw that the bus was veering off to the side, then I grabbed the wheel," he said. "It was just adrenaline pumping."
As he took the wheel, 12-year-old Darrius Clark applied the brakes and the pair were able to guide the bus to safety.
Darrius's 13-year-old sister Kayleigh ran from the back and called 911. "I was scared, but also I had to help," said the eighth grader.
She said the call handler could hardly hear her as so many children were screaming.
With disaster averted, 15-year-old Destiny Cornelius noticed the driver was holding a nebuliser and administered the medicine while 13-year-old McKenzy Finch held her head.
McKenzy also used the driver's phone to tell transportation authorities what had happened.
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Driver Leah Taylor, after her recovery, said the children's quick thinking on Wednesday prevented a potential disaster.
"I'm grateful for my students. They're the ones that saved my life and everybody else's on that bus," said the 46-year-old.
The principal of Hancock County Middle School, Dr Melissa Saucier, praised her students' quick thinking.
"They didn't wait for somebody to step in, they stepped up themselves, and that says a lot about their character," she said.
The kids were honoured at an assembly on Friday and will next week be treated to a lunchtime trip to a restaurant of their choice.