Boris Johnson and Kelly Brook at Potters Fields Park for Sky Ride launch

Tens of thousands of cyclists are expected to take part in the Mayor of London's Sky Ride which will be held on Sunday 5 September.

The 15 km route for the 2010 free mass-participation cycling event will be closed to cars and buses and open to cyclists between 9.30am and 4.30pm.

Riders will be able to experience the heart of London with a circular route running from the Tower of London to Buckingham Palace via the City of London. This year for the first time the route will also take riders through Parliament Square.

"It's brilliant," says Kelly Brook. "I did it last year and it's for all ages and all abilities.

"It's a lovely day out – very social – and even if you're not a keen cyclist it's a great day out with family and friends."

The annual event was launch in 2007 during Ken Livingstone's mayoralty when it was known as the London Freewheel. Now the London Sky Ride is part of a nationwide series of city-centre cycling events organised in association with Sky.

The Mayor has designated 2010 as London's 'year of cycling' to coincide with the launch of the Barclays Cycle Superhighways and Barclays Cycle Hire schemes this summer.

Mr Johnson was also pressed by reporters to respond to claims in The Sunday Times that he had threatened to quit City Hall if funding for transport schemes in the capital was cut by the coalition government.

He dismissed the reports as "an August story" but stopped short of an outright denial.