The officers are protesting against proposed changes to their pay and conditions.
Some 20,000 officers from all 43 forces across England and Wales are thought to be taking part in the first police march in the capital for more than four years.
More top news
London Underground claims unions refused to discuss a revised pay offer.
Lutfur Rahman was also ordered to disclose detail of income and expenditure.
10 years on, George Psaradakis has given his first interview, recalling the events of July 7 2005.