Report from the list http://lists.riseup.net/www/info/cm-london :
This was my first Mass, and I loved it!
Looking forward to the next one, already blocked on my calendar.
I discovered a few secret London corners, great itinerary.
I would prefer for the group to stay more compact, many people were straddling and got lost, which is a shame.
I’m in two minds about the red-light jumping. I’m ok from a safety/legal perspective, but I don’t want to give “cyclists” a bad name. In terms of advocacy, if someone’s considering taking on cycling and they see us, some may say “cool”, but many others will think, “how dangerous/reckless” etc.In any case, sometimes I got the impression that we were going a bit out of our way to piss motorists off by blocking traffic unnecessarily. It ties back to staying more compact.
Finally, I’d appreciate leaving on time.
Anyway, overall very happy to have joined the group! Oh, and thanks for insisting on not using Facebook, haha!
Itinerary: Southbank, police, Waterloo bridge, Kingsway, High Holborn(?), Trafalgar Square, The Mall, Constitution Hill, Piccadilly, Haymarket(?), Trafalgar Square, police, Strand, Waterloo Bridge, York Road, Leake Street (graffiti tunnel), police, The Cut, Southwark Station, Quietway 14, Southwawrk Bridge, Upper Thames Street, party split Old Billingsgate riverside/Tower of London entrance (maybe more).
It was a great night for a ride around London.
It seems that some police presence at SouthBank led to a very early start, so there were loads of people looking for mass after it had left.
Police was there right on time for 7pm so everyone made a very quick run. I don’t think a mass ever started so early. 
If you want a better report, posts yours to londoncriticalmass@riseup.net or to the list http://lists.riseup.net/www/info/cm-london
Opinions….
Critical Mass was never about blocking the streets but being a part of the streets. The norm is usually to cycle around non stop at a leisurely pace so everyone could stay together.