The Queen joined Second World War veterans to mark the 70th anniversary of VJ Day, when Japan surrendered and brought an end to the conflict.
Tributes were paid to thousands of Allied soldiers, sailors and airmen who sacrificed their lives as a service was held at St Martin-in-the-Fields church in central London, before a memorial event was staged at Horse Guards Parade.
The Metropolitan Police encouraged people to continue with their plans to attend the events following media reports that extremists were aiming to attack the commemorations.
Security was tight around the church in Trafalgar Square where the Queen - dressed in a dusty pink outfit and hat - was joined by the Duke of Edinburgh, and the Earl and Countess of Wessex.
Hundreds of veterans gathered later on Horse Guards Parade for a Drumhead commemoration, which was attended by the Prince of Wales, the Duchess of Cornwall and Prime Minister David Cameron.
Royal Marine buglers and percussionists from Portsmouth piled up their drums to form a ceremonial altar at the centre of the parade, replicating the practice used by troops on the front line.
Charles, Mr Cameron and Royal British Legion chairman John Giddings laid wreaths by the Drumhead, while Camilla, dressed in mint green, watched from the royal box.
Crowds applauded as a Dakota, Hurricane and a current RAF Typhoon fighter flew past the parade. The world's oldest surviving Royal Navy Swordfish bi-plane was due to lead the flypast but did not take part due to a "last minute minor technical issue", a Ministry of Defence spokesman said.
Actor Charles Dance read Rudyard Kipling's Mandalay - a favourite marching tune for many in the 14th Army in Burma.
Veterans, civilian internees, their descendants and families with serving members of the armed forces, then marched from Whitehall and through Parliament Square to Westminster Abbey - passing the statue of the 14th Army commander Field Marshal Slim - in a special 70th anniversary parade.
Along the route they were supported by military bands, and the final part was lined by serving military personnel. A reception took place in the grounds of the Abbey, hosted by the Royal British Legion.
Veterans met Charles and Camilla at the lively party where a band played to more than 1,000 people.
Gordon Smith, 95, from Rotherham, talked to Charles about how he watched the atomic bomb fall on Hiroshima.
He was in the Royal Electrical and Mechanical Engineers and was a prisoner of war from 1942.
"We heard this plane. We went and had a look out and this plane was overhead and the next thing we saw something floating down," he said.
"We didn't know what it was. It exploded in mid air and then there was a great big cloud like a mushroom. And that's all we saw."
Speaking about the commemorations, he said: "I think it's been marvellous."
Joseph Fisher, 93, from Newcastle, was in the Royal Army Medical Corps, and hailed the day as ''fantastic''.
He said the reception of the crowd during the parade was ''unbelievable'' and it brought a tear to his eye.
''I never expected anything like that,'' he said.
He added: ''It's very important because you mustn't forget what happened.''
He also chatted with Camilla, which he described as a ''highlight''.
Mr Cameron said thousands of people had died and many others "suffered appalling injuries and torture" during the conflict to "preserve our freedoms".
"I feel my generation hasn't had to suffer anything like what these incredibly brave people went through," he said.
"It is completely humbling to think how these people suffered, to think how many people died, to think how brave they were and what they went through for our freedoms in this titanic struggle, it is truly humbling."
At the church service, a wreath was dedicated at the altar in memory of those who died in the fight against the Japanese and of those who died as a result of the brutal conditions in Japanese prison camps.
George Reynolds, 97, who joined the Royal Artillery as an 18-year-old in 1937, became a prisoner of war when Singapore fell and recalled the words that were said to him and his comrades that marked the end of their ordeal.
"For you the war is over," they were told. "I wasn't ecstatic," he said, adding that he was a professional soldier. "I just took it as it came."
Standing over 6ft tall, Mr Reynolds had dropped to just five and a half stone.
Reflecting on what it was like to land back on British soil, he said: "It felt great. It was nice to see green fields." He now lives in Newport, Wales, and has 10 great-grandchildren.
There were an 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.
More than 2.5 million Japanese military personnel and civilians are believed to have died during the war.