I had the same on the second generation car but done in a generic garage.
While the front brakes work nicely, the rear ones do not get enough use and seize. As a result, they wear without being used on heavy braking.
So I do not think the MOT guy is right as such but the rear brakes need regular maintenance to make sure that they are free.
The way to check that everything is right, is to touch the wheels after every stop. They should never boil hot even in the city and when you driving away from the city, they should be cold.