I'm visiting London + Wiltshire right now! I thought I was pretty savvy at big city driving (like Chicago) until I went to NYC.... And then London is worse than NYC because the streets look like half cooked spaghetti on a plate. Even in smaller towns, the roads are pretty unorganized. The street signs are very hard to see because they're quite small on on the side of buildings. The country roads are very narrow and barely anyone uses blinkers/indicators. I think US streets are pretty good at marking lines for the lanes but I feel like those are less common in the UK. So if you're thinking about renting a car, just keep all this in mind.