This is the reason I'd never take my car to anywhere but a council MOT centre as they DONT offer a repair service they are not going to go looking for things that they can make a quick buck on by saying it needs replaced. They are not going to be bias.
Also most council MOT centres work on 10min time slots so they don't have time to go through things "slowly" so they can actually miss things and pass when it wouldn't have. This happened me and a new fault was picked up when checking if he other fault was replaced. They tried to fail me but got this overturned by the MOT centre manager as I then requested a full FOC retest to make sure nothing else had been "miss" (questioning their working standards) the response was we are 2 busy to do that so as they refused a full retest there and then and prove of the original failures being fixed my MOT certificate was promptly produced.
Most branded dealers are billing close to if not over £100/hour including VAT so to see a quote of £660 isn't a surprise. £250 for 2.5 hours labourr then £400 for parts if using "dealer pricing" rather than your local autoparts shop.
I thought that an MOT has a minimum time the car must remain in the garage. I'm sure my MOT man said the test car must be in the garage something like 40 minutes. He's a good indi that so I'd have no reason to doubt him.