You can try and take the money and run however they will take you to court in the UK as there is an agreement between the Spanish and British tax offices.They will have their Euro of flesh. If you pop up on the UK radar of course.That having been said as a "Non Resident" Your Solicitor will retain 3% of the sale value and hand it to the tax man it depends on how much they think you have got away with that they pursue you for the rest.If of course the gain is less than the 3% retained you can "try" and get the rest refunded but it does take a while.Over 65 and a tax resident ie pay taxes in Spain and you do not pay CGT.This is why you should submit a tax return each year even a negative one ie no Spanish earnings.Once you have 3 years as such and are over 65 you do not pay as above.You can be fined up to 200 Euro for non tax return.This still applies if your pension is a civil service type ie Government pension and you are taxed in the UK. Tax is a minefield and you should get professional advice.

Try this web site it may help,The second is the UK tax office  :-/

http://www.abacoconnect.com/non-resident-taxes-in-spain

http://www.hmrc.gov.uk/international/spain-index.htm