Yes, Construction and Use regulation 98 allows a stationary vehicle to continue to run an engine in order to operate machinery where the running of the engine is necessary to power such machinery or equipment.
A copy of the wording of the regulation is as follows:
Stopping of engine when stationary
98.(1) Save as provided in paragraph (2), the driver of a vehicle shall, when the vehicle is stationary, stop the action of any machinery attached to or forming part of the vehicle so far as may be necessary for the prevention of noise or of exhaust emissions.
(2) The provisions of paragraph (1) do not apply:
- When the vehicle is stationary owing to the necessities of traffic;
- So as to prevent the examination or working of the machinery where the examination is necessitated by any failure or derangement of the machinery or where the machinery is required to be worked for a purpose other than driving the vehicle; or
- In respect of a vehicle propelled by gas produced in plant carried on the vehicle, to such plant.
It is advisable, though, that you instruct your drivers to switch off the engine when it is not required to power the machinery. This will not only save fuel but will cut down on the vehicle emissions and noise emitted from the vehicle and will hopefully lead to less complaints from members of the public.