Can I Still Go to Spain With a Negative Covid Test if I'm Unvaccinated?

No, from December 1st, Spain is temporarily banning entry to Brits who are not fully vaccinated fin response to the new variant of Covid-19. 

Before now, passengers from the UK were permitted to show either proof of vaccination or a negative test to gain entry into Spain, but from 1st December, only proof of full vaccination will be accepted(this applies to all over-12s). Passengers must have received their second dose of the vaccine at least 14 days before travelling to count as fully vaccinated.