Go to Ministry of Interior in Plaza del Campillo del Nuevo Mundo (near Puerta de Toledo) to be inscribed on register of Foreign Residents. Under European legislation, EU citizens do not require residence permits, these are no longer issued.Unfortunately as the British government is only now starting to issue them again, I don't have an ID card. This means that I should carry my passport every time I go out, which is rather a non-starter I think.
I was given an appointment several months ago. They attended to me quickly and there was no problem. Had to pay a €10 fee at the bank down the street.
I downloaded the fillable form EX-16 in PDF from the Ministry's website and saved it, then printed it out on paper, which was very efficient, I thought. Although PDF was at least tagged after a fashion, it had loads of accessibility errors; they obviously hadn't checked it at all. It was done with Acrobat Distiller. So much for accessibility of government websites. It was only created three months ago, in compliance with a law passed in 2007, so no excuse. The site proclaims its WCAG 1.0 AA, compliance, but then that's no surprise either.