Tensions are rising between the UK and Spain in a row over the future of Gibraltar, as the UK embarks on negotiations to leave the European Union.

The dispute intensified since the circulation of the EU's draft Brexit negotiating guidelines on Friday appeared to offer Spain a right of veto over Gibraltar's future trade relations with the bloc.

The move prompted fury in the UK, where ministers described it as "utterly unacceptable".

A former leader of the UK's Conservative party, Michael Howard, said on Sunday that British Prime Minister Theresa May would even be prepared to go to war to defend the territory, as Britain did with Argentina over the Falkland Islands 35 years ago.

Howard's comments followed an interview on Sunday by Michael Fallon, the UK's defence secretary, in which he said: "Gibraltar is going to be protected all the way because the ­sovereignty of Gibraltar cannot be changed without the agreement of the people of Gibraltar, and they have made it very clear they do not want to live ­under Spanish rule."

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Voters in Gibraltar, a strategically important rocky outpost at the entrance to the Mediterranean Sea, rejected the idea of Britain sharing sovereignty with Spain by 99 percent to 1 percent in 2002, but overwhelmingly backed remaining in the EU in June's Brexit referendum.

Spain ceded Gibraltar to Britain in 1713, but has long called for it to be returned.

Spain's Foreign Minister Alfonso Dastis on Monday called for calm.

Tone of comments

"The Spanish government is a little surprised by the tone of comments coming out of Britain, a country known for its composure," Dastis said during a conference in Madrid.

But the British government was angered further after Spain appeared to ease its opposition to an independent Scotland becoming a member of the EU, saying it would not immediately block such a move.

The Scottish independence drive - now resuscitated by the prospect of Britain's departure from the EU - is highly controversial in Spain because of the secessionist movement in Catalonia.

As a result, Madrid has long been seen as an obstacle to an independent Scotland joining the EU after Brexit. But its foreign minister, Alfonso Dastis, threw that in doubt on Sunday.

"Initially, I didn't think we would block it," he said in an interview published in El Pais.

Dastis did stress that Madrid would not welcome the disintegration of the UK and said that Scotland would have to apply for EU membership, a process fraught with uncertainty that is likely to take several years.

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Gibraltar's leader scolded EU Council President Donald Tusk on Monday for giving Spain a right of veto over the future relationship between the British enclave and the EU.

"Mr Tusk, who has been given to using the analogies of the divorce and divorce petition, is behaving like a cuckolded husband who is taking it out on the children," Gibraltar's Chief Minister Fabian Picardo told Reuters news agency in an interview.

Picardo said Spain was trying to bully Gibraltar and that the EU was allowing the bullying to happen, and said Gibraltar would not allow itself to become a bargaining chip in the Brexit negotiations.

"We are not going to be a chip and we are not going to be a victim of Brexit as we are not the culprits of Brexit: we voted to stay in the European Union, so taking it out on us is to allow Spain to behave in the manner of the bully," he said.

Picardo said the EU should remove the reference to Gibraltar from the draft guidelines. "Removal of the reference to Gibraltar would be a sign of good faith and goodwill," he said.