Remembrance Sunday to be marked at the Cenotaph
More than 10,000 military veterans and civilians will march past the Cenotaph later to mark Remembrance Sunday.
For the first time, their number will include representatives of a World War Two unit known as "Churchill's Secret Army".
The Queen will lead the nation's commemorations from Whitehall.
A two-minute silence will be observed by military veterans and senior officers, political and religious leaders and Commonwealth dignitaries.
The marchers will set off down Whitehall in London after the silence and the wreath laying ceremony. And services will take place across the UK at war memorials, as well as in other Commonwealth countries and at military bases abroad.
It follows a Festival of Remembrance at the Royal Albert Hall in London on Saturday evening, which included a surprise reunion between 10-year-old Megan Adams, who was performing as part of the Poppy Girls group, and her father Lieutenant Commander Billy Adams.
Megan, who had not expected to see her father for another three months as he has been serving with the Royal Navy in the Seychelles as part of an anti-piracy task force, burst into tears as he appeared on the stage.
Kerry Ashworth, whose son James was killed in Afghanistan last year and posthumously awarded the Victoria Cross for bravery, said Sunday would be a very special day.
"The job that they do is so hard and so tough and when somebody loses their life, it's just one little thing that you can do just to remember them for a few minutes."
The marchers have been assembled under the auspices of the Royal British Legion and will be headed by representatives of the Britain's war widows, former Gurkha soldiers and West Indian servicemen and women.
The biggest single contingent, 500 strong, will represent the British Korea Veterans Association: 2013 is the 60th anniversary of the armistice which ended the three-year Korean War, in which 100,000 British soldiers, sailors and airmen served, many of them national service conscripts, and in which more than 1,000 died.
There will also be nearly 200 members of the South Atlantic Medal Association, representing Falklands veterans, as well as members of associations for veterans of the Suez invasion, the conflict in Aden and two Gulf Wars.
Among groups marching for the first time this year will be 41 members of the British Resistance Movement.
Known as Churchill's Secret Army or the Coleshill Auxiliaries (from the village in Oxfordshire where they trained), they were volunteer fighters charged with going underground to continue the fight in the event of a German invasion of Britain in World War Two.
The contingents on parade include former members of Popski's Private Army, a special forces unit which fought in North Africa and Italy during World War Two.
Members of the Memorable Order of Tin Hats, an organisation for South African servicemen, will be included.
They will be joined by the British Nuclear Test Veterans Association and the Malayan Volunteers Group; civilian residents of Malaya and Singapore who joined up locally to fight the Japanese in 1940.
Blesma, the British Limbless Ex-Service Men's Association, and Combat Stress, which helps those struggling with post-traumatic stress disorder, will both be represented.
And the Shot at Dawn Pardons Campaign will be present. Its members won posthumous pardons for more than 300 British solders executed during World War One for desertion.
But some of the 219 contingents are a fraction of their size in former years: only six members of the Normandy Veterans Association and eight members of Far East Prisoners of War will be marching, a reminder of how few today remain with first-hand experience of World War Two.
The marching veterans will be preceded by serving members of the armed forces, including a largely female contingent representing the RAF.