Workers from the City of London Corporation and City of London Police gathered in Guildhall Yard to observe the two minutes' silence.
Workers also gathered in the Lloyds Building, where the service was observed with the ringing of the Lutine Bell, the laying of wreaths before the Book of Remembrance and a two minute silence.
In Trafalgar Square, after an hour of readings and songs, people were invited to place poppy petals in the fountain. During the two minutes, called Silence in the Square, traffic lights were set to red.
Whitehall was also shut off to traffic between Horse Guards Avenue and Parliament Square for a commemorative service to take place.
Among the regiments who lined the streets for the Whitehall ceremony were Gurkhas who had fought for Britain all... https://t.co/s39xpuad7N— Gurkha Brigade (@Gurkha_Brigade) November 11, 2015
Numerous businesses also observed the two minutes' silence. Staff at The Ritz were among them
Football teams including Arsenal marked the moment.
In Woolwich, the widow of Lee Rigby, Rebecca, and her son laid a wreath at the plaque to commemorate the soldier who was murdered in 2013.
And up and down the country, millions of people were silent as a mark of respect. The Princess Royal attended a service at the Armed Forces Memorial in Staffordshire.
And even further afield. The Prince of Wales and Duchess of Cornwall took part in a service in Canberra earlier today.
And there were representatives of the Royal British Legion in France too. David Bambridge, from Melton Mowbay, appeared on behalf of the British charity for commemorations at the Franco-British National Memorial in Thiepval near Albert, northern France.