A bit BR

I shouldn't have said 'speed limits' so sweepingly without stating what I mean--I mean speed limits as under the Road Traffic Regulation Act 1984:

http://www.dft.gov.uk/pgr/roadsafety/speedmanagement/speedlimits

Speed in Richmond Park is probably governed by park bye-laws instead, I would assume?

Royal parks have an entirely different set of laws, and the speed limits do apply. Additionally in a royal park you have to do anything reasonably asked of you by a police officer or park official.