"N" registered aircraft may be flown in a foreign country on a license issued by that country. You can fly it within the UK (only) with your UK issued license. You cannot fly it with the same EASA license if it was issued by a country other than the UK. To fly it in Ireland, you'd need a separate Irish license.
FAA 14 CFR 61.3(a)(vii)
Sounds like the aircraft is operated privately and not commercially on an AOC for reward or hire. What you as the pilot get out of it is between you and your priest. All the usual caveats apply (ref Cardiff footballer), but you gotta ask yourself what is wrong with the EASA/CAA system for such a proliferation of N registered aircraft being operated in Europe.