Cheers all. I did query the garage and got a good response back and feel more comfortable now. The main cost is in the parts as thought and they're being fair with labour.
Labour comes in at £123.12 + VAT,
brake pads at £48.50 + VAT,
the brake discs at £60.50 each +VAT,
the rear calipers at £168.94 + VAT each and the brake fluid which will be required with the caliper change at £40.83 + VAT. This comes in at a total of £671.33 + VAT which equals £805.60
I know those parts are expensive and can get far cheaper, but I'm happy to pay more knowing it has the very best parts and done by someone who really knows what they're doing rather than a kiwi fit monkey!