Cheers Chris
sent an email to the department of transport marked Urgent and they got back to me with more or less this:
"Vehicles used on the road must comply with the Road Vehicle (Construction and Use) Regulations 1986 (C&U). However, vehicles must also be maintained so as not to be a danger and Regulation 100 of C&U requires that motor vehicles and their trailers shall at all times be in such condition that no danger is caused or is likely to be caused to any person on a road. "
Also goes on to describe digital signage on mobile adverts which wont apply to me in this case.