Tax liabilities

First question would have to be : are you a permanent resident? i.e. you have more than 5 years continuous residency in Spain?

If the answer to that is “no” then you are not a Spanish resident as a condition of residency is that you spend more than 183 days a year in Spain.  Your residency will be voided.

If “yes”, then as a permanent resident you *can* spend up to 5 years continuous outside of Spain (as a UK passport holder, all other countries including EU get 2 years) *HOWEVER* I would suggest seeking advice because once again a condition of residency is that you actually reside in Spain.  If you are spending less than 6 months a year here every year, you cannot be held to be actually “residing” in Spain and again you MAY find your residency forfeit - please please seek advice on that from a lawyer with migration experience 

With regards the tax issue, you will not be liable for tax in Spain as you must be here 183 days to be tax resident.  You should be liable for tax in the country in which you are actually residing.  THAT BEING SAID, if you are on the Padrón here then that is a declaration of residency, that you actually *LIVE* at the address specified and AEAT can take that as a declaration of tax residency even if you are not physically here …

Your situation is fraught with pitfalls and I would urge you to seek professional advice