This article is from the Model Rockets FAQ, by Wolfram von Kiparski with numerous contributions by others.
From: firstname.lastname@example.org (Richard Osborne)
Well groups like AspireSpace (http://www.gbnet.net/orgs/aspire/) and
MARS (Middlesex Amateur Rocketry Society) in Southern England fly
vehicles up to K power without problem. They do always inform the
CAA first, to ensure a NOTAM is issued, but apart from that, there
never seems to be any problem, even with the police. Maybe certain
areas of the UK are more touchy about model rocketry than others.
I don`t think STAAR Research (http://www.gbnet.net/orgs/staar/) has
any problems with their numerous HPR launches in Scotland either.
I don`t know about the other UK group called SERFS.