Excellent advise Mr C. Unfortunately, it would mean moving from the part of the south-east I currently live in because as far as I can establish, there is no garage around here that meets all of your suggested criteria. There is certainly nowhere locally that does free re-tests at the moment.
The cam-belt needs doing on my car. Age and infirmity make it a job that I would struggle to do, although I have all the equipment needed, and the knowledge to do it. Although I am prepared to pay up to and including main dealer prices, I'm unable to find anywhere I would trust to do it.
One of my step-sons worked in the motor trade, firstly as a main dealer mechanic, and then as an AA patrol. He obviously has visited many garages, and seen them at work. He is unable to recommend a single one of them to me.
On the other side of the coin, I have twice had excellent treatment when having had problems whilst travelling. Both small establishments went well beyond what might be expected; I subsequently wrote letters of thanks to both of them. However, one of them was in Oxfordshire, the other in North Yorkshire, so not terribly convenient for me from here!
Chris