Leaving caravan in France/Spain

Wouldn't have thought so but you may have insurance problems with the caravan so check.  I assume that you would have a UK plate on the caravan the same as the towing car.  Don't forget that in Spain if the total length of the outfit (car + caravan) is greater than 12 m you will need a long vehicle sign on he caravan.

I do know that Caravans/trailors towed by Spanish tuggers are subject to an MOT test, not sure what they test for and judging by the state of some Spanish caravans, not a lot, they also have their own number plate displayed, not that of the tugger. 

" Don't forget that in Spain if the total length of the outfit (car + caravan) is greater than 12 m you will need a long vehicle sign on he caravan."

good point, i have these, the Guardia carry stick on ones in their cars, if you get stopped and you do not conform, you have 2 options, face an on the spot fine or give the nice man €30 and he will give you the stick on ones 

I don’t know the situation in Spain, but it is common for UK owners to store caravans in France, and campsites there often provide that facility. Towergate insurance company is one which will provide cover for British caravans stored in France -  but that company  will want to know the proposed storage before they agree to it.

For instance 150 British caravans stored at this British owned campsite in France. 150 vans at 360 euros a year - you do the math,  but seems quite a money spinner.