Traveling by ferry can be fun and it's one of the most environmentally friendly ways of visiting Spain, so the budding ecotourists out there should consider this excellent option of visiting Spain.
See also: Index of Ferries to Spain
The price of a ferry from England to Spain is comparable to a budget flight and you have the advantage of being able to take your car with you. But, of course, unless you are staying in northern Spain, you'll have further transport costs when you get to Spain.
The Plymouth to Santander route takes 18 hours. The Portsmouth to Bilbao route takes 11 hours.
These ferries to Spain can be booked here: Book Ferries to Spain.
Ferry Routes from England to Spain
Ferry Routes from Spain to England
Transport in Spain
Once you get to Spain, you'll need to get around. These links may be helpful to you.
If you are taking the Portsmouth to Bilbao route, there is plenty to do in Bilbao before you head off for the rest of Spain.