Bad luck mate.
I got so confused once by speed limits changing randomly outside Agadir, they were bound to get me. There was a speed trap just after the fifth or sixth speed change, and I won myself an on the spot fine. Or that's what I should have got, but when I got my wallet out to show the copper my licence, a load of crisp notes fell out. The coppers beamed and his eyes lit up like a Christmas tree and suddenly it was understood that I was offering him a bribe, and in an instant I was too far into the deal to get out. £30. Not my finest hour.
As you've gathered, we've sealed a new deal with Spain allowing them to send speeding tickets back to us in the UK. It came into force last year - here's the announcement from giv.uk website: Agreement in the form of an Exchange of Notes between the United Kingdom of Great Britain and Northern Ireland and the Kingdom of Spain on the Reciprocal Recognition and Exchange of National Driving Licences and on the Exchange of Information on Road Safety Related Traffic Offences (publishing.service.gov.uk).
I don't know what other countries it applies to.