Britain's biggest cycle race kicks off in London on Sunday.

The Tour of Britain, which covers 500 miles over six stages, starts at Crystal Palace park.

The main event - the prologue time trial - begins at 3pm, with riders racing against the clock at one minute intervals through the park, reaching speeds of nearly 40mph.

Up to 20,000 spectators are expected at the free event, which also features races for amateurs and semi-professionals. Top riders will include Mark Cavendish and Geraint Thomas, who competed in the Tour de France, and former British road race champion Roger Hammond.

Steve Taylor, of Transport for London, which is sponsoring the event, said: "There will be something for everyone and with the Tour de France still fresh in people's minds we are expecting a great day out. We hope this will encourage even more people to take up cycling."

As well as the headline event there are youth races, a women's grand prix, and the TfL London Grand Prix for semi-professional clubs. Racing starts at 9.30am.

Tour of Britain spokeswoman Deborah Egerton said: "This is a great opportunity to see some of the world's top professional cyclists and up-and-coming British riders."

Another cycling event, the London Hovis Freewheel, is on 23 September, including a cycling festival in St James' Park.