I don't think I dreamt this up (though its possible) but I'm sure I heard/read that there was a population of Rocky coast breeding pipits that looked more like Water. I think it was Galicia
What might be interesting is my notes from breeding Water Pipits in the Pyrenees and the Alps. I have sometimes noticed that breeding birds in the Pyrenees have slightly broader streaks on average on the breast sides and flanks than those I see in the Alps. This may account for WPs that seem to have broader streaking in winter? Food for thought and further research maybe (or not).
Well all I can add is that if I saw the bird in photo 1 on the south coast of the UK I would have it down as a Rock pipit 100% - and I think I wouldn't be alone. I can see only features that point in that direction (dull brown rump, streaked back in addition to those stated above) and none in the other. I have compared it with the Rock pipit photos I have and the ONLY feature that differs is the legs on this bird are really dark brown, whereas in my photos they are only mid-dark brown..... if anything a pointer towards Rock vs. Water as I understand it.
The few Water pipits I've seen in the UK looked like photo 2.
Given Little auks turn up in central England is it not possible that a vagrant Rock pipit can turn up in Central Spain?
Genuinely intrigued .....and willing to be educated.
Mick