After multiple trips with kids in tow to the UK we've found that we prefer to bring our own seats and strap them in. Why? The kids know the seats, we know that we bought quality safe seats, we know how to strap the seats in, and we know how to routinely check them to make sure everything is snug and tight. We've also found that seats rented from the car rental companies vary from Britax seats (yeah!) to weird contraptions made by a train spotter and his 10 left thumbs while drunk and sleeping amongst the sheep. Plus, rental companies won't install the seats - which brings us back to the ease of putting your own seats into a new car versus borrowed ones. We've also found out that some EuropeCar stations rent out Toyotas with the LATCH system so it's easy to stick the seats in. Also, most Hertz cars come with some sort of seat system, so we've stuck with Hertz the last few years. We've fortunately never been stopped by the car seat police, so I can't answer on the legality of our seats. I figure if they're good enough for US regs, the FAA, and us, then we should be okay. If not, we'll pretend we don't speak English. One last note, don't forget the cars there are much smaller than in the states, so don't expect to fit a big baby seat and mom and spare luggage in the back seat unless you're renting a people mover.