I think Cueta is a critical point here. If England does not remain in Gibraltor, then wouldn't Spain entirely control the western mouth to the Mediterranean? Their presence in Cueta is a military one--at least when I was there about 25 years ago, armed police lined many of the streets.
Spain (under the Socialists) is now playing kissy-face with Morocco, and I would not be in the least surprised if Ceuta and Melilla are handed over to Morocco. That would mean that the western mouth of the Mediterranean would be at least partly controlled by Morocco, which is, in my opinion, not a good idea.