Thats a question or three. A car in the UK needs to have an MoT test which your pal could get before you bought the car. It needs to have insurance - plenty of companies on the net but not being a colonial I do not know how they view colonials. Then finally there is an annual tax to use the vehicle on the road and this cannot be transferred owner to owner any longer. Lest you feel inclined to ignore these laws, we are the world capital for state-run CCTV cameras and there is no doubt they would spot you. Whether they would physically catch up with you is a different issue. The best way round all this is for your pal to MoT test, tax and insure the car himself with you as named driver on the insurance and do the legal ownership handover when you ship the car back to the USA.
For you yourself you need a driving licence that is recognised here. I think the US one is but I dont know for sure.
Finally, TVRs are notoriously unreliable, the company went bust and I really wouldnt like to risk driving one outside the UK. Plus there will be some states in the US where you could not put the car on the road for eco reasons. California would be doubtful for example.
Best advice? Forget the whole thing.Too many potential pratfalls.
P.S. I am not an expert on the various rules above - this post is my understanding of how things work, so if you do decide to go ahead - check everything carefully.
Last edited by howard; 01/09/15 12:21 PM.