Trading Standards are the official channel I would suggest for a grievance as a first line of defence/attack, the offending company will certainly take you seriously when they realise you have engaged their services. An independent engineers report on the vehicle with copies to both parties is a good idea if significant money is involved.
Employing this line of approach you may get action instead of speculation IMHO.
Good luck.
Last edited by 4/4sportsfun; 21/12/14 06:35 AM.