From reports from the roads through glympse: www.glympse.com/!criticalmasslondon
This was the route:
Waterloo Bridge, west to Marble Arch, south from Hyde Park, past Victoria and Albert Museum, across Cromwell Road, past South Kensington Station, right on Brompton Road, South on Old Church Street, left on Chelsea Embankment, A3212. After Battersea Bridge, the A3212 is called Grosvenor Road, heading East. Held on the roundabout junction with Vauxhall Bridge; then North on Millbank, to Parliament Square. North to Whitehall, Trafalgar Square, Strand, Waterloo Bridge, BFI IMAX roundabout, back to meeting point in South Bank.
Windy and cold evening.