The flag raising ceremony - with Tower Bridge as a backdrop - will begin at midday, with Londoner Christine Ohuruogu, the Olympic 400 metres champion, and Chris Holmes, Britian's most successful Paralympic swimmer, accompanying Johnson.

 

Johnson said: "Raising the flags together at City Hall marks a historic moment for London, following the return of all our athletes who performed so brilliantly at the Beijing Games.

 

"The flags signal our dedication and commitment to ensuring that the London Games in 2012 will be a sporting feast open to everyone."

 

Also taking part will be London 2012 chairman Sebastian Coe, Olympics Minister Tessa Jowell MP, plus 1948 Olympians, 2008 medal winners and 2012 hopefuls.

 

There will be representatives of the British Olympic Association, British Paralympic Association, London 2012, UK Sport and the Olympic Delivery Authority, plus London Assembly Members and other politicians, community leaders, Borough leaders and local schoolchildren.

 

Coe will be at the event having taken part in a special London 2012 hour of Martin Creed's Work No. 850 installation at Tate Britain, to help kick off the celebrations for the launch of the Cultural Olympiad.