I have been through this too. Years ago, I bought an older shape BMW 320i from a house dealer in Salisbury. When I got the car home, I found that the horn did not work and the exhaust manifold was blowing like a b!tch. I tried calling the chap that sold me the car, but he was always unavailable. I thought then that he must have had some kind of deal with a local garage to turn a blind eye to certain things on cars that he had up for sale. So I called the Ministry Of Transport and they arranged a garage local to me where they would appraise the MOT with the original inspector present. It took about an hour and not only was the manifold deamed dangerous, but the sills were rotted out as well and a shock absorber was leaking. As a result, the inspector lost his ticket, but I did not lose my MOT.
I left the car with the local garage to sort out what had been picked up, who then proceeded to rip me off.
Hurn Airport Services, they are called. Avoid like the plague, rip off theiving b@stards.
The manifold turned out to be the older 6 into 1, which are known for warping. BMW sorted this out by producing a 6 into 2 into 1, thus relieving the stress. What thegarage did was to remove the manifold and have it skimmed for 250 quid.

Without informing me! They then told me about the later manifolds which are readily availble in scrap yards which I could have bought for 30 quid or so. I ended up paying over 400 quid in repairs for a car that cost me 700.