Here is yet another example of a vehicle sound system being allowed to be played loudly outside of Parliament, with plenty of police around, but bicyclists during Critical Mass are not allowed to play theirs at all, not even softly.

 http://www.criticalmasslondon.org.uk/video/socpabus.rm

Voice interview with police.
Http://www.indymedia.org.uk/en/2007/09/380072.html

Photographs of police cautioning a cyclist with a sound system while
videoing him.
Http://www.indymedia.org.uk/en/2007/08/377541.html

Photographs of police mistakenly stopping a sound system outside of
SOCPA zone.
Http://www.flickr.com/search/?q=socpa%20%22park%20lane%22&w=all&s=int

Video of van playing loud music in Parliament Square while being
ignored by cycle police. A longer clip can be made available.
Http://www.indymedia.org.uk/en/2007/04/368988.html

Video of police in an attempt at clarification of the law.
Http://www.indymedia.org.uk/en/2007/04/366898.html