And don't sweat driving on the other side of the road. It becomes second nature very quickly. Where you'll have the most trouble is simply entering the vehicle from the correct side.

That said, stay out of London proper unless a native is driving . . . it's abso-frickin-lutely nuts. Getting in and out of Heathrow isn't a big deal, but take public transportation if you need to enter the city.

PS. If you're renting a car, SatNav is a godsend and worth every penny. One less stressful thing to worry about.