It's an offence to do so
Road Traffic Act offence of 'quitting' which is when a person leaves their vehicle's engine running while they are not in it, any one know the act, I can't find it
Regulation 107(1) of The Road Vehicles (Construction and Use) Regulation 1986 (S42 of the RTA 1988)
Regulation 107(2)(a). This states that no person shall cause or permit to be on any road any motor vehicle which is not attended by a person duly licensed to drive it unless the engine is stopped and the parking brake is effectively set. Exemptions to the requirements of this Regulation as to the stopping of the engine include a fire brigade vehicle, the engine of which is being used for any fire brigade purpose.
Just thought id throw that in
