In no way does part NCC dictate any requirement for a UK validation
Absolutely correct, this is a Part-FCL requirement.
Part -FCL came into effect in 2012, and states that crew of aircraft operated by an entity based in an EASA state must hold EASA licences or validations. Article 12.4 states that member states
may elect to defer the implementation of this. Note
may not
must. The thing that has been put back again and again is the date to which they can defer.
So the CAA has decided that the deferral beyond August will only apply to PPLs effectively, and apparently some other countries have not taken up the deferral at all. The UK's policy therefore applies to aircraft whose operators are based in the UK, France's to French ones, etc.
Letters by an MEP sying that they meant the regulations to mean something else are as much use as yesterday's newspaper if you have an inspector grounding your aircraft because you do not meet the requirements that are actually there. If they meant them to mean something else then they should have written something else.
Having said that, I can't see how there is any way of enforcing it at a ramp check level, it can only be done at an operator audit level. I don't see there being many of those for Part-NCC operators for a long time.