Every once in a while, usually during a domestic Spanish scandal, Spain decides to kick up a fuss about British rule of Gibraltar. Eventually it all comes to nothing. Nevertheless, it's worth going through the main reasons why Gibraltar is not Spanish, and won't be anytime soon.
1. It is British "in perpetuity"
Lets be clear from the outset. Spain's legal claim to Gibraltar is weak. It does not dispute the Treaty of Utrecht of 1713, the document which formally ceded the Rock to the British "in perpetuity".
Instead it bases its argument on territorial integrity, calling Gibraltar a colonial relic (hypocrisy you may cry, but don't worry, we'll get on to that point).
Knowing that its legal case is weak, the Spanish government also refuses to acknowledge Gibraltar's territorial water, or its airport which is built partly on reclaimed land and on the isthmus, which was not explicitly covered by the treaty.