The formalisation of the ATO/DTOs has put an unambiguous responsibility onto them.
As an instructor I have flown in a lot of pilot maintained aircraft. Some have been maintained and kept to the highest standard, perhaps well above any statutory regulations that are demanded. At the other extreme are those that I would not fly. It isn't uncommon for instance to come across a lack of maintenance of things such as the aircraft instruments: "I don't bother with the ASI or the altimeter, they haven't worked for a long time, the GPS tells me all that I need to know". How then can an instructor teach the correct use of the flight instruments if they do not work or are not there?
The ATO/DTO has a responsibility to ensure the safety of its students, even from themselves. The school is obviously responsible for the efficacy of the training. Once employed by the school, even on a casual basis, then the school has a 100% responsible for the safety of the aeroplane. The only way an ATO/DTO can be certain of the aircraft safety is certification by a licenced engineer. The school should therefore hold all the mandatory paperwork including the logbooks during the training and ensure that they are in full compliance throughout the time used by the school.
All the DTO needs to do is add the aircraft to the yearly review they have to send to the CAA.
That is a ridiculous thing to say. Compliance does not come about on one day a year.