Time Out says
Sometimes referred to as Poppy Day, the Sunday nearest to November 11 is designated Remembrance Sunday each year. It's been observed since the end of World War I and is marked by a parade and wreath-laying at the Cenotaph in Whitehall to honour those who gave their lives in WWI and WWII and subsequent conflicts. The ceremony is attended by the Queen and other members of the Royal Family, who join members of the Armed Forces, ex-service men and women, political leaders and representatives of faith communities for a two-minute silence at 11am. The last post is sounded before the wreath-laying and a short religious service. Everyone is welcome to watch the March Past from the pavements along Whitehall and Parliament Street and orders of service are distributed by the Scouts. It's a good idea to arrive early for what is always a dignified and moving occasion (Whitehall is open to the public from 8am).
Spectators are asked not to take photographs during the two-minute silence.
On Friday November 11, Silence in the Square (10am-11.45am) is an opportunity to mark the two-minute silence on Armistice Day collectively in Trafalgar Square.