While in general the accepted unwritten rule is 'buyer beware' this has no basis in law. If you sell a vehicle whether privately or get it trade, the seller is obligated in law to ensure the vehicle is roadworthy (mot passable is the generally accepted definition although other factors do come into it) whether sold with an mot or not. Most of us, as we maybe have little knowledge of vehicles, rely on the honesty of the seller to inform us of problems (which they are obligated to do, it is there responsibility to know the exact condition of what they are selling and to give full disclosure of such.)
The following is part of the law...
'The Road Traffic Act makes it illegal for anyone to sell a car that is not roadworthy. This applies equally to private sellers and car dealers. Anyone who sells an unroadworthy car may be prosecuted and fined £5000. If you are found driving an unroadworthy car, you can also get points on your driving licence, and even be fined.
If you've been sold an unroadworthy car, you can get the seller to put the problem right. You can also report them to Trading Standards, who may take action against them.'
Look it up if you would like more info. I feel for you, I too have been ripped off (although I would not label krave with this term as I don't know him and his intent with regard to this) with a car I bought. I scrapped it as it wasn't an economical repair and I wasn't aware of my rights in law at the time.
You would have to have an engineer assess the vehicle and if shown to be unroadworthy you can take the seller to court although you first need to give the seller the opportunity to rectify the problems.
The 'buyer beware' principal is good in that it can save us a lot of trouble if we get the vehicle assessed before buying. Honest sellers will not usually mind the vehicle being looked over by a professional. Well worth paying a bit for a pro to look at it if spending a lot. If I'd payed 1000s then I'd take action to sort it out.