Yes, Shirley, certainly most of the bigger sites can be booked, and those beside the beaches may need to be booked but only in the busiest six weeks.
If they have a website they will either have an online booking form or an e mail address,for bookings. Even some of the smaller municipal campsites can be booked by an e mail to the local Mairie.
But luckily there are many, many sites away from the coast in France which never need booking at all, even in the summer. I never bother to book. But Spain I don't know about. Sorry.
Spanish sites may well be busy with long stayers in the sunnier regions. The popular ones can get booked up.
In France, you need to take a list of possibles, depending on the routes you may use. I replied earlier to another thread that on the ACSI card scheme, there are 54 French sites open for business on Christmas Eve, and that does not include any 'independent 'sites not in the scheme of course.
Shirley, When I replied before I hadn't realised you were going out in mid winter. I think at that time of year , even if you don't make formal bookings, I would phone your chosen sites across France, the day before you get to them, to make sure they really are open and haven't gone away on holiday themselves. Take care.
Don't forget to leave a review of the French and other European campsites you have visited!
You don't need to book on the journey down but you should consider booking your site in Spain if you intend to stay on the coast for a while. If you are not sure where you will end up or not particular where to stay then you don't need to book as you should get in somewhere.
There are sites open in France and there are a few listed in the Camping Clubs Winter Brochure if you can get one.
In previous years we have gone straight to Camping Acacia at Tours and then Laroulette at St Jean de Luz on the French/Spanish border.
We go Portsmouth to Caen on the 2.45 ferry and stop at Des Capuccine that night. From there it's off to Le Fituriste at Poitiers, then onto La Roulleta. Form there it is over the border on the N121 into Spain.
We don't book any sites, except the main one in Spain.
Les
------------- The worst day fishing is better than the best day working
Shirley, I head off in November travelling through France from Calais and ending up on the south coast of Spain in January. I used the ACSI books to pick my sites en route and emailed all of them, each and every one came back to me within a day or two saying they had made me a reservation but that I did not need to book and could have just turned up, even the site I end up. at (Los Gallardos) pencilled me in for a six week stay without requiring a deposit, indeed not one asked for any money up front, good luck and have a good trip, beats the UK winter 😉😎