You are still using a UK licence in France (unless you have a French issued licence), and so the UK ANO would still be applicable.
I don't think the UK ANO would be applicable. The UK ANO can only be applicable within the territory of the UK (& IoM and such), or to a G-reg aircraft flying abroad (as established by the Chicago Convention). It can not be applicable to someone flying an F-reg in France, for instance. Laws don't work that way. In order to fly an F-reg you have to have something that is acceptable to the French authorities.
That's why there will be an article in the French laws, equivalent to the one I quoted from the ANO, that renders a UK licence valid for flight in an F-reg aircraft. It's the logical consequence of the implementation of JAR-FCL, many years ago. But since the French law renders the licence valid, from that point on it's the French law which applies, and which may grant further privileges and set further restrictions.
Now obviously the French are not that silly, and just like elsewhere there will be a further clause somewhere in French law that states that all the original UK restrictions on your licence will apply. But my point is: It's the French who decided to put that clause in, and thus the French who may grant exceptions to that clause. Not the UK authorities, as they have no jurisdiction.
By the way, this is the exact same reason why the letters that Fuji refers to, are written by the French DGAC, and not by the UK CAA.
The reason for the specific clause "within the UK" in the ANO is to prevent people from exercising their IMC privileges outside the UK in a G-reg. That's a situation where the ANO does have jurisdiction (as agreed in the Chicago Convention), and the ANO wants to prevent that. But there's no need for the ANO to prevent people from exercising the IMC privileges in an F-reg, as the ANO doesn't have jurisdiction over that situation in the first place.
Question: If you have a valid UK IMC rating, are you allowed to exercise the privileges of that rating, within the UK, in an F-reg?
(I think not, as you need a licence issued or rendered valid by the DGAC to fly in an F-reg. And the DGAC - apart from the letters that Fuji mentioned, and that were issued on an individual basis - doesn't render an IMC rating valid as there's no French equivalent.)
Anyway, it's all very hypothetical, especially now that EASA has taken over. Although I remain highly interested in the documents that Fuji has. Fuji, is there no way you can quote the relevant bits and pieces from that document, while protecting the identity/innocence/virginity/whatever of the parties?