I may have got the wrong of the stick but and probably have but,
I was talking to at 747 captain of Atlas who flies from stansted. He said he was approached by one of the UK based airlines because he is also a TRE. He would have had to convert his license but apparantly there is a quick route via ireland.
Something about Ireland having some kind of grandfather rights and only needing to do the HPL exam..... Even if this is wrong its worth looking into.