As a matter of interest what level ELP do you have on your French licence? On what grounds do they refuse the Level 6 on your UK licence, did they require an additional assessment?
From the basic regulation:
Article 11
Recognition of certificates
1. Member States shall, without further technical requirements
or evaluation, recognise certificates issued in accordance with
this Regulation. When the original recognition is for a particular
purpose or purposes, any subsequent recognition shall cover
only the same purpose or purposes.
I could understand them not accepting Level 6 on a UK JAA licence because the level was not printed on the licence. It is printed on an EASA licence!