I agree, in essence, but if it has a brand new MOT, and it starts and drives, in court the dealer would simply say, "What is the problem?", so fit for purpose and of satis quality is a bit dodgyThe Consumer Rights Act 2015 requires dealers to supply goods that are fit for purpose, as described and of satisfactory quality. Its the law, and as a dealer, they should know it. You are perfectly within your rights to ask for your deposit back.
HOWEVER, it is described as a 7 seater which it ain't and with that he has them by the bollox as that comes under the Trade's Description Act or whatever it is called now. AND as a 7 seater, it isn't fit for purpose.
don't think he'll have a problem.