Notdunroamin

If you get stooped in a roadside check, or get in an accident where the Guardia are called, and claim to be a tourist then you'll almost certainly be asked to prove it either by producing your passport (which you're legally required to carry) which will have a stamp noting your date of entry either into the Schengen area or Spain itself. You could well be asked to show your return ticket too.

A lack of those will immediately mark you out as an illegal immigrant from where it will very rapidly go downhill!

For those who plan to continue winging it don't forget that UK photocards expire after 10 years (or age 70) and even if you have an old paper one which expires on your 70th birthday to be valid then needs to be accompanied by an IDP which can only be got from a UK post office on production of that licence.