The problem is that the police were not allowed to use the drone and themselves committed a crime in the process.
The Civilian Air Authority, or CAA, regulates air space in the UK and had changed regulations as of 1/1/2010. The new regulation states that all UAVs or unmanned aerial vehicles must be licensed before use. From the Guardian:
The CAA introduced new statutory regulations on 1 January 2010 which requires all UAVs to be licensed by the CAA before use. Since the force has known of the change in regulations all UAV flights have been suspended and will remain so until the appropriate licence has been granted.
I guess the police forgot to get a license before playing with their new toy.