Last week I had an American friend over and we were talking about driverless cars, and she said she thought they might work in the USA, but having seen what UK roads are like, she was very skeptical they'd work there, so maybe Google should try it!
For example, many roads in tows date back to roman times, and are too narrow for two-lane traffic. You need to look far ahead and work out when exactly you need to duck into a gap behind a parked car to let oncoming traffic through, and when to go for it when you have right of way so as not to block traffic in either direction. And if a block does occur, will it mount the pavement (sidewalk) to free things up, or know when it's time to back up and give in?
The UK has very few towns laid out in a grid, and most roads are twisty, and narrow, other than motorways. Can a driverless car cope with such terrain? If Google really want to prove their technology is better than a human, let them bring their cars over to the UK. If they work here, I'll be impressed.