From reports from the roads through glympse: www.glympse.com/!criticalmasslondon

This was the route:
After Waterloo Bridge, off to Soho, Long Acre, Drury Lane, Museum Street, Oxford Street, Marble Arch roundabout, Park Lane but inside Hyde Park, Hyde Park Corner, Picadilly, Picadilly Circus, Trafalgar Square, Orange Street, Charing Cross Road, William IV Street, Chandos Place, Maiden Lane, Southampton Street, Strand, Adam Street, John Adam Street, past Waterloo Bridge, Victoria Embankment, Blackfriars Bridge, Stamford Street, IMAX roundabout, just South of Waterloo Bridge.