OK, that shows my ignorance of European political divisions. Is a crown dependency not still considered part of the UK?
No - they live in a weird grey area, the UK is responsible for them internationally but they're not part of the UK, for instance they weren't in the EU even before Brexit. Which is why they make such good tax havens. It's essentially a feudal relationship that goes back to the 13th century and before, the link is via the Queen personally - not in her role as British monarch. Compare that with the British Overseas Territories which is what we call our remaining colonies because we don't want to call them colonies, where the link is effectively through Parliament. I guess the nearest US equivalent is the relationship between the US and Guam or the US Virgin Islands, but with more history and a bit of the legal weirdness of DC.
In contrast, France is more unabashed about calling its colonies part of France, with representation in Parliament and everything. It also means that places like Martinique are part of France and hence the EU, which makes it a popular place for scientific conferences as you can get travel grants from Brussels for travel to conferences within the EU - and obviously it's more convenient for North Americans to get to.
There was one lab I worked in where two colleagues took advantage of this to go to a conference in Martinique. The more ...ernest... one came straight home. But you had to fly via Paris and all of France was on strike for one reason or another, so they endured a journey from hell, luggage going missing, the works. Whereas the more chilled colleague took their tent and bummed around a Caribbean beach for a week, then came home after the strikes had finished, the journey went smoothly. There's a lesson there!
I'm going to be in trouble for not getting somewhere in Brittany though. It makes sense that it's in the Celtic part of France, the building in the foreground could easily be a chapel in Scotland, but the tower behind just looked all wrong to be in the UK.