thanks Backpacker, very helpful.
Being a permanent resident of the UK, it's been incredibly difficult to get this sorted out.
What the French authority is now saying is that if my SEP renewal is done in the UK, it needs to be done by a flight instructor registered with them (ie based in the UK but with the ability to issue SEP renewals for licenses issued in France). This makes it incredibly difficult to get done as I cannot imagine this is common. What's the point of having an EASA license if they will only renew it with an instructor based in the country where it was issued? Surely the standards are the same across the UK and France if they are both EASA member countries, I cannot understand why they wouldn't accept a UK CAA FI to do my renewal checkride.
To your point though, they have confirmed that once everything is in order, they will transfer my license to the UK CAA so that it can be administered from there.