Well, I am looking at the ANO, in which the FI rating and its privileges are defined in law.
I am also looking at JAR-FCL 1.300 in which it appears to suggest that the FI rating is valid for instruction in any JAR state. France and the UK have both signed up for mutual recognition of JAR-FCL1, so I would imagine that clinches it. N'est-ce pas Mr van Rental ;-))