Remembrance Sunday: 100 years since WW1 began
The Queen has led the nation in remembering service personnel who have died during conflicts, as Remembrance Sunday services are held around the UK.
A two-minute silence was observed before the monarch laid a wreath at the Cenotaph in central London.
Events are being held across the UK and abroad, including in Afghanistan.
This year marks the 100th anniversary of the start of World War One, 70 years since the D-Day landings and the end of Britain’s conflict in Afghanistan.
David Cameron said the anniversaries made the commemorations “particularly poignant”.
Security is visibly tighter in central London this year.
Scotland Yard said there would be “appropriate and proportionate” policing at the Cenotaph after four men were arrested on Thursday in west London and High Wycombe in connection with an alleged Islamist terrorism plot on British soil.
Mr Cameron said: “Today we stand united to remember the courageous men and women who have served our country, defended our freedoms and kept us safe.
“We remember all those who have fallen and those who have risked their lives to protect us.
“We owe each and every member of our armed forces and the families who support them a tremendous debt – one that can never be repaid – and I pay huge tribute to their bravery and resolve.”
World War One Centenary
After dusk falls, images of falling poppies are to be projected on to Big Ben, officially known as Parliament’s Elizabeth Tower.
On Saturday, the Queen and other members of the Royal Family joined veterans and the public at the Royal British Legion’s annual Festival of Remembrance at the Royal Albert Hall in London.
Elsewhere today, a service will be held at the National Memorial Arboretum in Staffordshire.
In Glasgow, a two-minute silence will be observed at the cenotaph in George Square, while in Edinburgh a parade will take place from the castle esplanade to the city’s stone of remembrance.
Scotland’s First Minister Alex Salmond will be among those laying wreaths, and a ceremonial gun will be fired.
In Wales, the national service will take place at the Welsh National War Memorial in Cardiff.
And Secretary of State Theresa Villiers will lay a wreath on behalf of the government at the Cenotaph at Belfast City Hall.
Tower of London Poppies
Thousands of the Tower of London ceramic poppies are to tour the UK to enable more people to see parts of the popular artwork.
The installation of the 888,246 poppies will start to be dismantled by a team of about 8,000 volunteers on Wednesday.
The tour will last until 2018 before being permanently based at the Imperial War Museums in London and Manchester.