Thousands of people showed up at Anzac Day services in London and across the United Kingdom to honour and remember those who have fought, died and continue to serve.

The dawn service at Hyde Park Corner, near the Australian War Memorial in London, was attended by Anne, Princess Royal.

Catherine, Princess of Wales, also attended a wreath-laying service at the Cenotaph, and the commemoration and thanksgiving service at Westminster Abbey.

Head of Australian Defence Staff Air Commodore Matthew Harper said the United Kingdom’s historic Anzac connection made it a special location to mark those who served in the European theatre in both World Wars.

“Many of our Anzacs set sail for the battlefields of Europe from British ports. Marking Anzac Day here in London is to stand close to that history and acknowledge the deep ties between Australia, New Zealand and the United Kingdom,” Air Commodore Harper said.

Among those braving the crisp London morning were two British brothers with connections running back to Gallipoli. They made the journey from outside Manchester.

Stephen and Paul Crooks, both former British Army soldiers, stood in the crowd wearing replica medals belonging to their grandfather, a Queen's Lancashire Regiment soldier.

“He was wounded at Gallipoli and crawled away and survived,” Stephen Crooks said.

“That's why we are here.”

A group of 20 Army cadets from The King’s School in western Sydney also attended the dawn service before marching in the wreath-laying service at the Cenotaph.

“We have been visiting some of the World War I and II battlefields, including Flanders Fields, and are here this morning to represent the school and the previous old boys who fought in those battles,” Year 11 student Hugh Miller said.

'In a world that is increasingly uncertain, the values of mateship, loyalty and standing by one another remain just as important as they were over a century ago.'

Year 10 student Austin Yang laid the wreath at the Australian War Memorial.

“I felt pride knowing that I’m laying something here as a way of remembering and giving thanks for those who gave their lives for the freedoms we have today,” Austin said.

Year 11 student Alexander Dohnt wore his great-grandfather’s medals at both services.

“It’s a privilege and quite an experience to remember and honour those fellow King’s boys who fought in the wars, as well as my own family’s contribution,” Alexander said.

After laying a wreath, Princess Anne signed the Book of Remembrance.

As the morning progressed, the focus moved to Whitehall and the Cenotaph, Britain’s national memorial to the fallen of both World Wars, where Princess Catherine laid a wreath honouring the Anzacs.

The day's ceremonies closed with a service at Westminster Abbey, which has its own deep connection to Commonwealth war commemoration.

The Grave of the Unknown Warrior inside the Abbey was the first such tomb to be established anywhere in the world, and Australians have gathered at it on Anzac Day for generations.

This year marks 111 years since the original Gallipoli landings – the first major military action fought by Australian and New Zealand forces during the First World War.

Air Commodore Harper said while Anzac Day commemorations were about remembrance, they were also about what the Anzac legacy means today.

“In a world that is increasingly uncertain, the values of mateship, loyalty and standing by one another remain just as important as they were over a century ago,” he said.

“The strength of our relationships with friends and allies continues to rest on those shared values and mutual trust.”