When do you think the Spanish are going to give Cueta and Melilla (two small Spanish enclaves in North Africa) back to Morocco? Probably the first of never.
That sounds like a suitable date to give Gibraltar back to the Spanish. As long as the Gibraltarians want to remain a British territory and the British are willing and able to protect Gibraltar from the Spanish, the Rock will remain British.
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.
i have no sympathy for the spanish anymore -- i used to be very much a fan.