Which is the best dealer?

I am looking to buy a left hand drive car in the UK. I am not sure where I should go to buy it though. Does anyone know a anything about left hand drive dealers in the UK? Which one is considered the best? I want one that really stands by their cars and will work to quickly resolve any problems that might come up with the car after we purchase it. Do the left hand drive dealers in the UK also repair these cars, or can I take them to any car repair place in the UK? Can anyone advise me?