One could easily see a role for UAV's in place of, say, Police Helicopters but surely the role of getting them accepted is a role for testing organisations to agree how to sign these things off and convince those that need it that these are safe - or can be made safe?
As has been mentioned before, there are two fundamental issues here. Firstly 'lost link' in which the UAV loses the uplink and/or the down link to the ground control station. Not an insurmountable problem, as the UAV will be programmed to enter an autonomous 'return home' mode, whilst the ground control station will start searching for the UAV to re-establish control.
The second issue is 'See and Avoid', especially whilst the UAV is in the 'return home' mode. This is fine in a military controlled danger area, in which all aircraft have transponders and are in communication with one air traffic controller. In VFR airspace, however, it would put the onus on every aircraft owner (gliders paragliders, microlights, LAA aircraft etc) to add an expensive piece of hardware to enable the UAV to 'see' them, and to communicate with a central point, so they can be diverted out of the path of a wayward UAV. Needless to say, mandatory transponders have met with huge opposition from the light aviation community as the aircraft owners would have to pick up the tab to enable a cost saving for a potential UAV operator. There is also the issue of multiple transponders in small areas of airspace, as might happen near a gliding competition.
No doubt there are people in the UK addressing these issues, as it does seem wasteful to see a police helicopter with two 600hp engines being used simply to support a camera ball that a 120hp UAV could do just as easily and hopefully a lot more quietly.