Meet 10am at Cutty Sark Gardens or 11am by Southwark Needle at the south end of London Bridge. Take part in the fifth annual Christmas Day bike ride, a leisurely tour around the silent city and London's parks. You can dip out when you feel you've had enough, or stay the course for refreshments by the river in Putney, a late lunch in Edgware Road, and a pub visit at the very end.