So I now see - thanks. What I'm really interested in is any reasonable place to leave the boat over winter on the Gironde. Also do you need any qualifications for coastal cruising in France.
As long as you are British flagged, you do not need any boating qualifications for COASTAL cruising. As soon as you go inland (normally defined as the first obstruction to navigation such as a bridge or lock) you need an International Certificate of Competence (issued by the RYA) which must be valid for the appropriate type of boat and MUST HAVE the CEVNI endorsement for Inland Waterways rules. If you already hold an ICC, you just need to do the CEVNI test which is a simple multi-choice test.
Also don't forget you need either Part1 or SSR registration for the boat itself......and the French certainly do check! Suggest you contact RYA for the full works.