I agree about the logging of hours providing properly recorded and, if appropriate, certified (a letter from my employer was sufficient).
Presumably the two most important factors will be firstly, would the LPC skills test for the foreign licence meets the standards of the JAA one in respect of all areas to be tested, and secondly are the qualifications of the "foreign" TRE conducting the test and signing you off acceptable to/recognised by the CAA?
Much depends where you are headed I suppose....darkest africa vs. hong kong for instance. Perhaps the new company employs ex-pat TREs from europe who, with the prior agreement of the CAA, could if necessary tweak the skills test and also sign you off for both licences? Doubtless you could quickly check this out with the prospective employer, and ask whether they have prior experience of your situation.
Whichever the case, I think a call to the CAA FCL department is unavoidable.