Soldiers walk during a change of guard outside the Convent building in the British overseas territory of Gibraltar, historically claimed by Spain, March 29, 2017. REUTERS/Jon Nazca

LUXEMBOURG (Reuters) - There will be no change to Gibraltar’s sovereignty without Britain’s consent, Foreign Secretary Boris Johnson said on Monday, while his Dutch counterpart called for calm after a British politician raised talk of defending the outpost.

“The sovereignty of Gibraltar is unchanged and is not going to change, and cannot conceivably change without the express support and consent of the people of Gibraltar and the United Kingdom, and that is not is going to change,” Johnson said on arrival at a meeting of EU foreign ministers in Luxembourg.

A former leader of Prime Minister Theresa May’s Conservative party said she would even be prepared to go to war to defend the territory, as then prime minister Margaret Thatcher did with Argentina over the Falkland Islands 35 years ago.

Asked by reporters if Gibraltar could become a military issue, Dutch Foreign Minister Bert Koenders urged everyone to keep their cool in Britain’s exit negotiations from the EU.

“You can now see how difficult the divorce is,” Koenders said. “Let us be cool and carry on and not use too harsh language. Let us negotiate, I think that’s the most important.”