Why can’t I vote?

This post is a whinge.  I was listening to Radio 4 the other day (via Internet radio) and apparently prisoners in the UK don’t have the right to vote.   There was a report or something from the European Union saying it was a breach of their human rights.  Now I don’t want to comment on the rights or wrongs of prisoners being able to vote.  What has pissed me of for many years is that I don’t have the right to vote and neither do millions of people like me.
I live and work in Spain, I pay my taxes here, I have bought a home here, my wife works and pays her taxes here, and 99% of everything I own is here.  In other words Spain is home but I cannot vote and it is not just me but every expat living in another country (that includes the Spaniards living in the UK).
We can vote in European elections and we can vote in local elections but not national ones, not the ones that determine how our taxes are spent.  Well that is not strictly true I can vote in national elections back in the UK, where I don’t live, don’t have a house, and don’t pay taxes.  But I don’t vote in the UK because as far as I’m concerned I don’t have the right to vote there.

Why; in the European Union with all its brave words about mobility etc. can’t I vote where I live and pay taxes?  Should we take up the banner once by earlier British imigrants “NO TAX WITHOUT REPRESENTATION”?
If anyone is aware of a lobby group or a member of parliament (national or European) who is taking this up please can they let me know.