The CAA are completely entitled to pursue the slightest technical breach of the ANO.
What they need to do is explain why they are suddenly vigorously pursuing matters which they have known about for years and had ample opportunity to do something about.
Every time a Cirrus files an IFR FP via CAS, anybody who sees that FP and has as much as opened a general aviation magazine or been to any airshow over the last few years will be aware that the aircraft probably doesn't carry an ADF.
Then there is the N-reg stuff, with the Dennis Kenyon prosecution and some others that aren't public yet. The CAA have been perfectly aware for years that training in N-reg planes has been done, completely openly, at a number of outfits around the UK, with examiners coming over openly from the USA.
Perhaps a political decision has been made to make N-reg life as hard as possible, without breaching the ICAO treaty obligations. Certainly all this fits that interpretation.