Had a lengthy conversation with the manager of the Boldon car clinic when picking up my GTD after repairs. They're approved repairers for very few insurers, despite doing a cracking job on mine and having an excellent reputation. He said the main reason for that is that to gain insurer approval, most insurance companies want them contracted to a blanket price for repairs, and that was commonly in the region of £1300, and they couldn't refuse a job.
Smart repair to a door with a small dent? £1300 please Mr Aviva.
Car been hit by a bus, with a £3k bill for parts alone? I wish you were giving me more than £1300 for this Mrs Sheilas Wheels.
With blanket bills like that there will be winners and losers, but mainly losers - who's going to blow their excess (and NCD if it isn't protected) on a £400 repair to allow the body shop to score for £900? No wonder corners are commonly cut with insurance company approved repairers.