Expensing a car in UK

Get a lawyer or a solicitor.

my interest buy a costliest car in the world that might be nice for me.

If you're in the UK, the government will do you over somehow if they really want to. Even if it meant using a loophole or dome 99890088 year old law.
A dangerous game to play.

If its r&d, theres a lot of blurred lines, youre technically right in saying that if you buy it for the purpose in research and you make that 10p, and declare it, you then can dispose of the cost as expense. But when you make a website to solely research the car the lines become even more blurry. There was a similar case with a guy at my ex job putting his server costs down as research as he was trying to start up a new cryptocurrency, as far as I remember tax man said no purely because the servers were too much for the cause. I think the same would apply to you. The way id put a car down is by declaring that you need to meet clients regularly with receipts provided, helps inflate your assets a bit as well. But as you said only part of the cost can be covered