From what I remember an MOT only says it's compliant on the day of the test. Have had it happen more than once when a brake pipe has gone within a few days after testing. Would say lower would be the sameExpense aside of the tests and the things that they reveal, it is quite comforting to have an MOT on my truck and car every year to make sure that it is safe to drive and that everything works.
Similarly for the Loler tests on my loaders although I am annoyed that they will ground one if that stupid piece of plastic paper on the dash board is missing for whatever reason.