Spain’s foreign minister has vowed to "plant his flag on Gibraltar,” as his government launches a diplomatic offensive aimed at convincing the international community that the Rock cannot carry on as a functioning British outpost after Brexit.

Speaking on Spanish state television late on Wednesday night, José Manuel García-Margallo replied to Gibraltar Chief Minister Fabian Picardo’s mockery of Spain’s proposal of joint sovereignty for the British Overseas Territory.

“No way, José,” Mr Picardo said at the United Nations in New York in a direct jibe at the Spanish foreign minister. “You will never get your hands on our Rock. Never.”

“I won’t put my hands there, I will plant my flag,” was Mr García-Margallo’s response as he outlined the benefits of joint sovereignty to Gibraltarians, who he said will otherwise find themselves shut out of the European Union.