What about the 'vivienda'? Doesn't that allow for a five-year lease with the option of inflation-only yearly rent increases?
That's what the Real Estate agencies are telling us.
This is from HMCR :

I]Tax Treaties in force - Spain
UK/Spain Double Taxation Convention signed on 21 October 1975 as amended by an Exchange of Notes signed on 13 December 1993 / 17 June 1994