I found The Car Buying Group from being the highest quote through the comparison site Motorway.co.uk. They were friendly and straight forward. There were no hidden costs or charges and they paid what they'd quoted (within about ten minutes), despite my car being rather shabby. I asked if they could collect the car the next day before my tax needed renewing, and they obliged. They were very easy to get hold of on the phone when I wanted to ask a question, and the subcontractor who collected the vehicle kept me up to date on ETA. A very good stress-free service.