It is all about theway the CAAs rules and their implementation have changed. Up until about 7 or so years ago there was a list of antique aircraft that could be imported and placed onto permits.
This lead to a lrge number of aircraft being imported and permits considerably outnumbering CoAs. The CAAs rules were then changed. Any imported aircraft not homebuilt, and with any sort of existing certificate of airworthiness could only be imported onto a CoA. The import trade collapsed overnight.
Paying the CAA for them to devise a build standard for a 50 year old aircraft is just about impossible. This is the situation that exists today. If it is on a permit you can remain with it, if its on a CoA you're stuck with it.
I suspect the PFA were going through one of their periodic internal squabbles when all this went through, because from memory it all came as a bit of a surprise.