The European Union has infuriated the British government by putting the future of Gibraltar at stake in talks over the terms of Brexit.
In a surprise move, it said Spain should be given an effective veto in discussions about the status of “the Rock”, a British overseas territory for three centuries.
The row blew up just 48 hours after Theresa May reassured MPs, as she triggered Article 50, that she was “absolutely steadfast in our support of Gibraltar”.
She also insisted that its position would be fully covered in negotiations running up to March 2019, when Britain is due to leave the bloc.
Spain’s long-standing claim to sovereignty over the territory has caused enduring tensions between the two countries, with periodic claims by Gibraltar that Spanish craft have encroached into its waters.
The EU’s initial draft negotiating guidelines said any Brexit agreement should not apply to Gibraltar without “agreement between the kingdom of Spain and the UK”.
The wording suggests that the territory should not be included in any deal secured by Mrs May without the explicit approval of the Madrid government.
Brussels officials confirmed that the guidelines meant that “only one side of the argument” would be represented by the EU if a dispute about Gibraltar’s status broke out between Britain and Spain.
The first minister of the self-governing territory, which voted last year by 96 per cent to 4 per cent to remain in the EU, this week warned that Gibraltar must not become a bargaining chip, pawn or victim in Brexit talks.
The Tory chairman of the all-party parliamentary group on Gibraltar, Jack Lopresti, accused Spain of using Brexit as “a fig-leaf for trouble-making over the status of Gibraltar”.
He said: “It is shameful that the EU have attempted to allow Spain an effective veto over the future of British sovereign territory, flying in the face of the will of the people of Gibraltar.”
The Labour MP Mary Creagh, a member of the Open Britain group, said supporters of hard Brexit should be “ashamed that their actions have destabilised the situation in Gibraltar”.
Tom Brake, the Liberal Democrat foreign affairs spokesman, said: “Confirmation that Gibraltar’s future must be agreed by the UK and Spain shows just how damaging the Government’s hard Brexit will be on this strategically-important British territory.
“Theresa May must urgently produce a plan that protects the citizens of Gibraltar, including their businesses and communities.”