90 day rule.

It depends if you want to come back, not just to Spain, you could get a Schengen Entry ban – The Members of the bloc can ban people from re-entering if overstayed for a longer period than 90 days. 'Bans are applied for a period of three years or even more'. 

'The 90 rule is about the 'Schengen Area', not the country you are staying in, they keep data on your entry and when you leave' 

https://www.schengenvisainfo.com/news/brits-overstaying-eus-90-180-days-rule-to-face-penalties/

Thank you for that warning.

Glad that's useful, it's worth remembering Brits are 'no longer EU citizens', when you enter the Schengen area we are a 'third country', so you may as well be arriving from the US. These countries treated as one - Austria, Belgium, the Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Italy, Latvia, Liechtenstein, Lithuania, Luxembourg, Malta, the Netherlands, Norway, Poland, Portugal, Slovakia, Slovenia, Spain, Sweden and Switzerland, 'so the 90 day stay applies to the whole cluster'. When you enter any of the listed countries you are considered to be entering one territory & the '90 stay starts then'. When you arrive as a no-EU citizen they check you into 'Schengen' as an 'international visitor'. It's a separate Schengen data system, so you could arrive, check in Malaga, travel to France fly back from Paris, but rather than being in France it will just be a departure from Schengen. 

Note - Link - Travel documents of non-EU nationals should be systematically stamped upon entry and exit from the Schengen Area.

https://www.axa-schengen.com/en/schengen-border-control