Veterans of World War Two are taking part in events to mark the 70th anniversary of VJ Day, when Japan surrendered and the war ended.
A memorial event has been held at Horse Guards Parade, attended by the Prince of Wales and Duchess of Cornwall.
The Queen and Duke of Edinburgh earlier joined the PM and former prisoners of war at a remembrance service at St Martin-in-the-Fields church in London.
David Cameron said it was important to “honour the memory of those that died”.
In Tokyo, Japan’s Prime Minister Shinzo Abe and Emperor Akihito observed a minute’s silence at a service.
On Horse Guards Parade, veterans and their families watched a fly-past of military aircraft – a Spitfire, Dakota and Hurricane of the Battle of Britain Memorial Flight and a Royal Navy Swordfish, together with a current RAF Typhoon fighter jet.
Actor Charles Dance read the poem The Road to Mandalay, by Rudyard Kipling.
The poem was set to music and became a favourite marching tune for many in the 14th Army in Burma, now known as Myanmar.
Veterans, war widows and members of their families then marched from Horse Guards Parade to Westminster Abbey, accompanied by marching bands.
Members of the public lining Whitehall applauded as the parade went past, with many of the veterans waving union jacks.
Wreaths have also been laid at the Cenotaph on Whitehall.
At the scene – BBC correspondent Robert Pigott
The service at St Martin-in-the-Fields was a poignant commemoration of those who died in the war against Japan.
Many of the thinning ranks of veterans of the conflict arrived in wheelchairs, medals glistening in the watery sunshine.
With survivors of the conflict now in their 90s the day has the feeling of a last hurrah.
There were stirring hymns, a piped lament, and moving readings, including a recitation of the Kohima Epitaph by 92-year-old John Giddings who fought in the Far East, “when you go home tell them of us, and say for your tomorrow we gave our today”.
After the service veterans recalled friends lost in the Far East and still grieved to this day.
But the mood lifted as they emerged into bright sunshine in Trafalgar Square, to the ringing of church bells, and began to celebrate still being, as one put it, “alive and kicking”.
The service at St Martin-in-the-Fields remembered the estimated 71,000 British and Commonwealth casualties of the war against Japan, including more than 12,000 prisoners of war who died in Japanese captivity.
The Reverend Dr Sam Wells, vicar of the church, told the congregation: “The struggles, the suffering and the sacrifice of the war in the Far East are a defining experience in our nation’s history.
“We stand in awe of those who were tried in ways beyond what most of us ever have to go through and greater than many of us can ever imagine.
“People who lost life, limb and liberty that we might know peace.”
And former prisoner of war Maurice Naylor spoke at the service, saying it was an honour to be joined by the Queen – “a veteran herself” – and members of her family.
He said: “How do I feel now? I feel lucky to have survived so long and still be able to address you. I feel sad for the families of those who died as a result of their captivity.”
Although fighting in Europe ended in May 1945, the battle between the Allies and Japan continued.
It was only after two atomic bombs were dropped on the country that the Japanese surrendered on 15 August that year.
It ended one of the worst episodes in British military history, during which tens of thousands of servicemen were forced to endure the brutalities of prisoner of war camps, where disease was rife and there was a lack of food and water.
Events have also been taking place across the UK to mark the 70th anniversary:
- A commemorative service was held at the Canongate Kirk in the Royal Mile, Edinburgh
- Church services have been held in Wales
- Wreaths were laid at a ceremony in Birmingham
- Prayers were said at services in Sunderland and Newcastle
- The cenotaph in Portsmouth hosted a service
A service will be held at the Far East Prisoner of War Memorial Building at the National Memorial Arboretum on Sunday.
VJ Day 70: The Nation Remembers is on Saturday 15 August from 13:00 BST on BBC One.