Youre probably looking at a week for a good course that will give you a good grounding in the basics. You could do a weekend but unless its just one or two subjects they tend to be taster courses.
If you were coming over from France then it might be good to find a course thats close to where youre coming into the country, that would mean less travel time in the UK. Have a look at the
list of schools here
Theres a bit of
guidance here as well
Its worth deciding for yourself what is the most important thing for you to learn, you may think that fire is very important, or foraging and cooking, shelter building. Or you may want to learn more about trees, tracking and animals. Theres a lot of good schools out there that provide what youre looking for, the hard work is finding the one that works for you.
Do contact them though and let them know that youre interested in coming on their courses, describe what youre after and when youre available, then let them tell you what they can offer you.
An alternative is to see if any of the members here on Bushcraft UK want to meet up with you sometime and share what they know, I know of a few members that have had good experiences doing this. Theres also the BushMoots that we put on a few times a year, people learn loads and its cheap.
Im sure that theres some courses running in France as well, Ill see if I can find the contact details.
I hope that you find somewhere and that you have a great experience with whoever you choose to go with, let us know how you get on.