Spain requires APIS from the UK
Although passengers arriving from the UK do pass through Spanish immigration and have to show their passports, I have never seen the passports being checked against any sort of list. For the past few flights (of many) the FR website hasn't even asked us for the APIS info., and I have the feeling it's either now derived from the check-in, or has been dropped as meaningless.
There are other ways for British to arrive in Spain which don't involve any form of ID check whatsoever.