As others have said Gib is British thanks to the Treaty of Utrecht and the population wishes to remain so under the UN Right to Self Determination. Unlike Melilla and Ceuta which are not covered by any treaty
AFAIK and the residents of which would rather not be Spanish!
Instead of political games and raising a few quid a far sighted Spanish Minister would be far better leading an advertising campaign in the UK to attract holidaymakers - something along the lines of 'come back to an old friend' to 'cash in' on the uncertainty thanks to various Arab 'seasons' - if Turkey kicks off again there would be real money to be made on the costas even if only 30% of the Turkish trade reverted to Spain.