Just found this on the net - thought it might be useful...
Laser Jammers and the Law
There is no law as yet regarding the purchase of a Laser Jammer or the fitting of one on a motor vehicle. However the first arrest was made in February 2003 regarding the use of a Laser Jammer. The person was arrested for "Perverting the course of Justice"
This offence is very serious and carries 7 years in Jail. It is normally used to deal with people that are caught out telling lies to get away with something or gain something without actually going to court and perjuring themselves in the witness box.
Usually, the offence used to deal with interfering with speed trap readings or the speed traps themselves, such as large notices before the trap advertising its position and it is in operation, would be 'Obstruction of Police in execution of duty'.
I would imagine that because this chap was deemed to be actively employing a system to purposefully demonstrate his ability to avoid prosecution, that the officer stopping him, used the offence of Perverting Justice to justify his arrest. Obstruction of Police has no power of arrest unless it is used in conjunction with the General Power under Sect 25 PACE 1984
Perverting Justice is an indictable offence (Crown Court only and very expensive).
Obstruction of Police is a visit to the Magistrates Court only and is much cheaper