True.
Admittedly, I don't have first-hand experience with vehicle-dependent foreign travel, but I can't imagine trying to cross a border (one where they do more than just wave you through) with a vehicle title that doesn't match the driver's passport. The only experience I have was driving my CJ-7 from Spain, through France, to Germany, but I had my US and international Drivers licenses, US title, US military license plates, and military travel orders. The only thing they didn't like was the 15 gallons of gas I was carrying in the back seat... "What, you think we don't have gas in France??"
I would like very much to understand how I could travel the world with a US passport, in a vehicle that does not have US registration/title/license plates.
Granted, you could (probably) title it in the UK on your tourist visa, but that registration (probably) expires when your visa expires or once you leave the UK, right?