but an hour with an Instructor every 24 month
There is no EASA requirement for an hour with an instructor ervery 24 months. One of the revalidation options under EASA is that you may use an hour with an instructor in the last 12 months of the validity of a SEP or TMG Class rating or you can do a Prof Check, or you can use another test such as a MEP revalidation or an IMC Prof Check. No BFR.
Using the N-REG would probably require the instructor to be dual qualified - that is EASA and FAA
The issue has nothing to do with the instructor, its the fact a pilot without a licence cannot legally fly the aeroplane in the UK.