A remembrance service marking the 50th anniversary of Sir Winston Churchill's funeral has taken place at the Houses of Parliament at the start of a day of UK-wide events.
The Havengore, the boat which carried the wartime prime minister's coffin along the Thames, will make the same journey again later.
Wreaths have been laid and a service will be held at Westminster Abbey.
PM David Cameron said the UK owed a "debt of gratitude" to Churchill.
He attended the commemoration event in Parliament and laid a wreath at the statue of Churchill in the Members' Lobby of the House of Commons.
Mr Cameron told the service: "If there is one aspect of this man I admire more than any other - it is Churchill the patriot."
A procession from the service ended under what has become known as Churchill Arch after it was rebuilt at his suggestion using fragments of stone remaining following a direct hit from a German bomb.
Tower Bridge will be raised at 12:45 GMT as the Havengore repeats its 1965 journey from the Tower of London to Westminster, after the funeral service at St Paul's Cathedral.
Once it reaches the waters opposite the Palace of Westminster, there will be special service and wreath laying in the waters.
Westminster Abbey will host a ceremony from 18:00 GMT, with flowers laid at the green marble stone placed there in memorial to Churchill.
BBC Parliament is broadcasting the BBC's original coverage of the funeral, narrated by Richard Dimbleby, with timings to match those of the day itself.
Sir Winston Churchill's funeral marked 50 years on
BBC News
39 January 2015
A remembrance service marking the 50th anniversary of Sir Winston Churchill's funeral has taken place at the Houses of Parliament at the start of a day of UK-wide events.
The Havengore, the boat which carried the wartime prime minister's coffin along the Thames, will make the same journey again later.
Wreaths have been laid and a service will be held at Westminster Abbey.
PM David Cameron said the UK owed a "debt of gratitude" to Churchill.
He attended the commemoration event in Parliament and laid a wreath at the statue of Churchill in the Members' Lobby of the House of Commons.
Mr Cameron told the service: "If there is one aspect of this man I admire more than any other - it is Churchill the patriot."
A procession from the service ended under what has become known as Churchill Arch after it was rebuilt at his suggestion using fragments of stone remaining following a direct hit from a German bomb.
Churchill's statue and the Churchill Arch in the Members' Lobby of the House of Commons. The room was extensively damaged by Second World War bombing, and was rebuilt afterwards in a simplified style. It was rebuilt at Churchill's suggestion using fragments of stone remaining following a direct hit from a German bomb
Tower Bridge will be raised at 12:45 GMT as the Havengore repeats its 1965 journey from the Tower of London to Westminster, after the funeral service at St Paul's Cathedral.
Once it reaches the waters opposite the Palace of Westminster, there will be special service and wreath laying in the waters.
Westminster Abbey will host a ceremony from 18:00 GMT, with flowers laid at the green marble stone placed there in memorial to Churchill.
BBC Parliament is broadcasting the BBC's original coverage of the funeral, narrated by Richard Dimbleby, with timings to match those of the day itself.
And BBC Archives is live tweeting the events of the day 50 years ago.
Churchill's grandson, Sir Nicholas Soames MP, said the Westminster events were a "fitting tribute" to his grandfather and a "strong reminder of all he did for his country".
Emma Soames, Churchill's granddaughter, added: "To me growing up he was a grandfather, but I came to realise at his death that he was so much more than that.
Churchill's great-grandson and granddaughter laid a wreath at his statue in Parliament Square
"The family are absolutely delighted that his life is being celebrated and his legacy expanded."
Randolph Churchill said it was a "proud day" and his great-grandfather would be "surprised but thrilled" at the commemorations. Along with Celia Sandys, Churchill's granddaughter, he laid a wreath at his statue in Parliament Square.
Mr Cameron described the country's prime minister during World War Two as a "great Briton" who must "never be forgotten".
He said the wartime leader's legacy "continues to inspire not only the nation whose liberty he saved, but the entire world".
BBC Parliament is broadcasting the BBC's original coverage of the funeral, with timings to match those of the day itself.
The footage, narrated by Richard Dimbleby, has been re-mastered for broadcast.
Journalist Martin Bell, who worked for the BBC as a junior reporter at the funeral, recalled moving around the crowds speaking to mourners.
He told BBC News: "What I remember is most of all the size of them - the sheer size of them, 10-12 deep all along the way. Very quiet, very dignified, almost devotional. It would be hard to imagine anybody now, however eminent, drawing that kind of crowd to his funeral."
He added: "It was unprecedented and we will not see the like again. The entire nation was watching."
Churchill led Britain to victory in World War Two
Members of Churchill's family will travel along the Thames on the Havengore, which carried his coffin in 1965
Fifty years on, the Havengore was being prepared ahead of the anniversary events. The vessel also carried members of the Royal Family during the Queen's Diamond Jubilee River Pageant along the Thames in 2012
From Friday, the National Railway Museum in York will display the locomotive - named Winston Churchill - which pulled his funeral train from London to Oxfordshire before his burial.
The carriages which carried the coffin and mourners will also be on show.
Sir Winston Churchill (1874-1965)
1874 - Born in Blenheim Palace on 30 November
1900 - Elected to Parliament for the first time
1908 - Marries Clementine Hozier in Westminster
1915 - Forced to resign from the Cabinet in disgrace after disastrous First World War Gallipoli campaign
1940 - Appointed Prime Minister with Britain again at war with Germany in World War Two
1945 - Loses the General Election to Clement Attlee's Labour Party despite leading the nation to victory in the war
1951 - Returns to Downing Street as Prime Minister after securing a narrow majority
1955 - Retires as Prime Minister due to ill health
1965 - Dies aged 90
Schoolboy failure to WW2 hero: The astonishing life of Churchill
Churchill began his career in the Army and he also worked as a journalist during the Boer War in South Africa, where he was captured and made a prisoner-of-war but managed to escape.
He served as first lord of the Admiralty and held various senior government roles before taking over from Neville Chamberlain as prime minister in May 1940, and leading the country to eventual victory over Nazi Germany.
He lost power in the 1945 election but remained leader of the opposition, and in 1951 became prime minister again.
He resigned in 1955, but remained an MP until shortly before his death. He also wrote numerous books, and in 1953 won the Nobel Prize for Literature.
Churchill's grave is in Bladon churchyard, near his birthplace of Blenheim Palace in Oxfordshire.
Churchill was given a state funeral
Crowded streets forced people to use every vantage point to see the funeral procession
Churchill's coffin was loaded on to a train at Waterloo station
The Pullman carriage used at the funeral is going on display at the National Railway Museum
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broadcast?
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BBC News - Sir Winston Churchill's funeral marked 50 years on
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