Veterans used semaphore to send a silent message along the Thames - it read: "War turns us to stone. In remembrance we shine and rise to new days."
Following a two-minute silence at 1100 GMT the Queen led the tributes to those soldiers who have died serving their country, by laying a wreath the Cenotaph in London.
In Edinburgh, veterans were joined by dignitaries, serving military personnel and members of the public at a service at the Stone of Remembrance outside the City Chambers.
The fallen were also remembered in Liverpool, where young and old came together at a service at St George's Hall.
Prime Minister Tony Blair was joined by the other main political party leaders at the Cenotaph in London. The service honours all those killed in conflicts since World War I.
More than 8,000 veterans made the annual pilgrimage, including those from the First Aid Nursing Yeomanry, queuing to leave their wreaths at the Cenotaph.
Air Chief Marshal Sir Jock Stirrup said: "The thing that always strikes me when this day comes round every year, is the way the whole nation rises to it."
First Minister Jack McConnell remembered the "fathers, sons, aunties, uncles, friends and comrades who were lost" at Scotland's national ceremony in Edinburgh.
One young boy watched on as a World War II Dakota aircraft dropped 100,000 poppy petals over the Remembrance Day service in Liverpool.
God Save the Queen was sung at the Cenotaph, while a service in Braehead, near Glasgow, opted for the less conventional Give Peace a Chance, by John Lennon.
World War I - 'the war to end all wars' - killed around 10 million people, with nearly one million British soldiers losing their lives. Only a handful of veterans remain to tell the tale.