In reply to punj:
The point of a double taxation treaty, as referenced in the link, isn't to make sure you pay tax twice, it is to ensure that you only pay one set of taxes. Once you have established which residency has priority you would register with that tax authority, and, if it is France, then register with HMRC as resident abroad. Unfortunately you can't (easily) choose the one that suits you best. If your UK employer pays through PAYE you would then have to reclaim UK tax from HMRC (nightmare) or agree with your employer to pay you gross and for you to declare your income to the French authorities. Failure to make this declaration would be a criminal offence so be sensible. Or something like that. I'm not an accountant so take this with a pinch of salt.