someone sent me £1mill accidently. should i keep quiet?

Haha You're kidding right? If It was accidentally. The guy that ''accidentally'' send you the money will come back for his money and you will get in trouble!

Possession being 9/10's of the law only counts in contraband. Sounds like someone at the bank is doing some money laundering and you don't want to be caught up in it by actively touching it. And once you touch it, you become liable for the taxes on it. Even when you have to give it back, you're unlikely to get a tax break, let alone any refund. And the bank WILL find the mistake and correct it. One case I saw took six months, but they found it.

You are woefully uninformed if you think that million Pound transfer to your account was legitimate. It is a common scam (Nigerian) and the bank will soon advise you that the funds are not there.

Purchase of anything with non-existand funds is a crime and you and your lamborghini will soon part ways. The auto back to the dealer and you to jail.

You can trace the account holder from whose account the amount was transferred into Your account .It might e a mistake .Ascertain from the account holder if he / she really intended to transfer the money o t your account and if so why. If the transfer is part of any fraudulent deal , you will be in trouble as the transfer can always be traced out .

are you kidding me?! you should feel horrible! you need to try to give the car back and get the money. what if that money needed to go to someone who was dying with cancer and they needed a transplant of some sort... i don't know! but you need to give that back.

Since you have broadcast your crime on the internet your question seems to be moot.