Your starting point should be the Sale of Goods Act and the Consumer Rights Act 2015, in particular section 9 of the latter. They can be found via google.
The trader can't exclude the contract term that they have good title to the car (e.g. they have not stolen it), so "no warranties" is subject to that (SoGA). If they have modified the car so as to make it dangerous I don't think they could exclude liability for death or personal injury (CRA).
s9 of the CRA says that the requirement for the goods (car) to be of satisfactory quality is subject to the terms in which it is described. Here they are saying either that they will sell only to a trade (not consumer) buyer or (more likely) that any buyer takes his/her chances and there is no warranty as to satisfactory quality. One can never be certain what a court might do, and if they knew the car was dangerous and did not expressly say so they might have problems, but otherwise they have probably made a reasonable effort at putting buyers on notice that they will have no responsibility for any problems with the car and that the buyer must check him/herself.
As you say, in that context it is not especially cheap. Only Range Rovers since 1988