The formal celebrations started with a procession from Buckingham Palace to Westminster Abbey at 10:20 BST.
In a break from tradition, King George appeared in the Diamond Jubilee State Coach rather than the older, more uncomfortable, Gold State Coach.
The procession moved along The Mall to Trafalgar Square, then down Whitehall and Parliament Street before turning into Parliament Square and Broad Sanctuary to reach the Great West Door of Westminster Abbey.
Outside the palace gates, there was a Guard of Honour, comprising about 160 members of the three armed services, with another 1,000 personnel lining the route.