I have been using Surbiton Town Cars for quite some time now without any problems.
This weekend I used them for a journey that I do quite often and it normally costs about £40. Last night, the driver decided that it was going to be more than double that. I didn't mind too much because he agreed to come and pick us up and do the return journey at quite a late hour.
He turned up on time and got us back quickly, but then asked for the same amount again! So, in total he was expecting to be paid £180 instead of £80 for the round trip!
We had been at a Christmas party so I expect he thought we'd be too drunk to notice! We weren't, and a swift call to the office sorted it out.
I expect that this was the actions of a rogue driver rather than the firm themselves, but it is worth watching out if you do use them.