I think it pays to develop a good relationship with a particular garage or mechanic / tester. The reason I use the one I do is that one of their mechanics used to work for an independent Landy specialist, and is a Land Rover driver himself. I've got to know the owner & testers over the years, and they're quite happy to let me fix little things on the spot, like the sidelight fuse that blew on the way to the garage last year, or the numberplate light I hadn't noticed. They also give my motor the once over before the MOT and advise me what I need to do before the test, and don't charge me any extra for it, and let me know if they notice any other work that might need done soon.