The Money Saving Expert website has this interesting article:
It's not the test fee but repairing the "fails" that usually costs a fortune. Yet little known council run MOT centres don't do repairs, so there's no vested interest to fail you and thousands report a massive difference.
Council-run MOT centres are set up to do their own vehicles (eg, buses) but must also open to the public. As they don't offer repairs, they've no vested interest to fail you. So MoneySavers' feedback like this is common: "My garage said repairs would cost almost £1,000 ... the council test centre passed it without any work needed." Find your council MOT centre.
Fleet Services (Camden Council), York Way Depot, Freight Lane, York Way, London, N1C 4BE 020 7974 3447