Under so-called "Open Skies" bilateral agreements between the U.S. and the E.U., the issue of licensing was supposed to be resolved by having reciprocity of licenses and credentials. After all, the conceit of the JAA licensing being somehow superior is pure balderdash. There is no reason at all--other than protectionism--for the UK and the EU to require a "JAA" license.
There should be, and there has been talk that there will be, a simple validation or conversion process, much like the one we finally saw implemented between the U.S. and Canada.