I was afraid you might ask that! In short, I think, unless you become autonomo (self employed), the answer is no…and you’d need to be a Spanish tax payer for that. More important is if you’d be able to continue paying in the UK. Have a read of this thread:
http://www.spainexpat.com/spain/forum/viewthread/3481/
the situations are different but there is a way, short term (E101?), that might help you if you are being “posted” to Spain. I would suggest you phone HMRC Newcastle or look at the HMRC website there are sections for people living and/or working abroad either full time or temporarily. Of course, you might just be able to carry on as you do now. If you want to remain a UK resident then the EHIC would cover you for medical care (emergencies and some other stuff) in Spain. You’d need private cover for run of the mill stuff but you would still be entitled to everything in the UK - if you are still resident there.
Again, this info is based on my own research so far.