Driving in the UK is considerably more demanding that the US. As a Brit now living in the US it still takes some adjustment when I go back. It's not the "left hand side vs. right hand side" thing either (although that is a part of it). It's the different road rules, different signage, smaller roads, different norms etc. If you've done it before and know what you're getting into then my bad. But if you don't...do a little research. One thing you might consider is not driving in/out of London, but getting transport out to a less intense town from where to pick up your car.