ceresale,
That's a tricky question. I might be over-simplifying, but as I understand it, if a chap loses his JAA Class 1 medical, then he won't be able to fly aircraft for remuneration on any of the European countrys' registers. That's on the condition that loss of medical was related to falling outside of JAA medical standards...
Whether the CAA might issue a restricted class 1 medical (restricting a pilot to perhaps flying day-time VFR commercially only within the UK, if there is such work) as long as they meet ICAO medical standards, I don't know. Anybody?
waterpau