Or you could just hire a brompton for £2.50 a day from a brompton dock
Can you buy that bike in Spain?
Decathlon will sell you something similar, and it looks like there's a couple of branches in Spain.
https://www.decathlon.es/
We're flying and renting a car. I could feasibly bring my folder on the plane, but I don't want to add to the OHs general stress levels with the extra juggling of luggage (which are always high when going on hols and I will suffer for it!).