We were called out to this vehicle in County Durham. On arrival the technician noticed 2 traffic wardens around it. The technicians first thoughts was that it was getting a big yellow fine sticker on the windscreen as the vehicle had broke down on double yellow lines.......in fact this was not the case but the vehicle did belong to the traffic wardens. They had been out working when they returned to their vehicle which did not start as good as it should have. When they got the vehicle engine started they drove until it came to a stop that's when they realised their mistake of "misfueling" their work vehicle. The traffic warden who "filled up the vehicle with the wrong fuel" has his own vehicle at home which is a petrol car giving him this reason for "filling up with the wrong fuel". The traffic warden was more angry that he had to pay for this out of his own pocket because the company said it was his fault. By the time "Forecourt Assist" received the call it took 15 mins to get to the vehicle and 25 mins to complete the job. These traffic wardens went on with their day.