Since you currently have the intention of moving to Spain then you would need to seek a Spanish policy as British policies will only cover you if you are going to spend at least 6 months of the year in the UK. When you move back to the UK, if you have no intention of returning to Spain, you will then be able to take out a British policy. I do not know either way whether this would be an option or not, but Santander are obviously a Spanish bank which owns Abbey, so they may have a policy which can cover both countries.
I hope this helps.
Adam.