Being a member of PVEC or PCUK helps with explaining it away at the roadside. Also need to have written permission, ideally from your local constabulary to order the battenburg kits... the firms simply won't supply it without.
It goes without saying that any blue or red lights (flashing or otherwise)/headlight flashers/sirens must be rendered inoperable whilst the car is on the road. This must be by removing the power connection outside of the passenger compartment. A switch in the glove box simply won't cut it...
Also any Police wording, web addresses, force crests must all be covered up when on the road along with signs in the rear window and on the drivers side saying 'Not in service'. The light bar must be covered unless the lenses are clear, and must be inoperable.
You also have to keep a log of every mile the car covers, with times/dates/reason for journey/where from and to/mileage in and out.
Worth noting that force crests are copywrited too, so you would need the relevant permission to obtain/use any
