Madrid has urged the UK to calm down over Gibraltar, after former Conservative leader Lord Howard suggested Theresa May would defend the territory as Margaret Thatcher did the Falklands.

The future status of the Rock emerged as a potential issue in Brexit talks after European Council president Donald Tusk circulated draft EU negotiating guidelines suggesting Spain would have a veto over the British overseas territory's participation in a future deal.

Prime Minister Theresa May has spoken to Gibraltar's leader, Fabian Picardo, to reassure him the UK remains "absolutely dedicated to working with Gibraltar for the best possible outcome on Brexit".

And Foreign Secretary Boris Johnson insisted there could be no change to its status without the consent of the people Gibraltar.

Arriving in Luxembourg for a meeting of EU foreign ministers, Mr Johnson said: "The position of the Government is very, very clear, which is that the sovereignty of Gibraltar is unchanged and it is not going to change and cannot conceivably change without the express support and consent of the people of the Gibraltar and the United Kingdom, and that is not going to change."

In a series of television interviews over the weekend, Lord Howard repeatedly compared the situation to the Argentine invasion of the Falkland Islands which led to war with the UK.

He told Sky News's Sophy Ridge on Sunday: "Thirty-five years ago this week, another woman prime minister sent a taskforce halfway across the world to defend the freedom of another small group of British people against another Spanish-speaking country, and I'm absolutely certain that our current Prime Minister will show the same resolve in standing by the people of Gibraltar."

Responding to his comments at a press conference in Madrid, Spanish foreign minister Alfonso Dastis said: "The Spanish Government is a little surprised by the tone of comments regarding Gibraltar coming out of Britain, which is a country known for its composure."

Downing Street said Brexit Secretary David Davis had met Mr Dastis for talks on Monday at the start of a pre-planned two-day visit to Spain and Portugal.

"The meeting, as I understand it, was very friendly and very constructive," a Number 10 spokesman said.

Mr Davis "echoed what the Prime Minister has already made clear in terms of our legal position around Gibraltar and the fact that we will be steadfast in our support for Gibraltar," he added.

While there was no reference to Spain's claim to sovereignty in the draft EU document released by Mr Tusk, the specific mention of a role for the Madrid government in deciding whether a trade deal would apply to the Rock has caused unease in Westminster.

Mr Picardo insisted that the people of the territory would not be used as bargaining chips in trade negotiations.

"The issue has been an attempt made by Spain in the draft to single out Gibraltar for negative treatment if there is ... a new trade deal in future between the UK and the EU which relates to services and which otherwise have been applicable to Gibraltar," the chief minister told the BBC.

"That's the issue. It's not an issue relating to Gibraltar's sovereignty."

Mr Picardo said it was "very helpful of Spain to have put this front and centre this early on in the process", rather than waiting until the final moment to throw a spanner into the works, as some had expected.

"I think Spain has made a huge error of judgment not just in putting this early on, but in effect denying their own citizens the application of that deal if they work in Gibraltar going forward," he said.

"After March 30 2019, absent an extension, any Spanish person working in Gibraltar will not have the benefits - if Spain gets its way - of any trade deal that might bestow benefits for workers."

He said there was "no question" of Gibraltar giving up its sovereignty in order to keep its membership of the single market.

"Sovereignty absolutely trumps membership of the EU," he said. "There's absolutely no question of Gibraltarians selling their sovereignty in order to have access to the single market in any way, shape or form."

Spain has a long-standing territorial claim on Gibraltar, which has been held by the UK since 1713 and has the status of a British overseas territory.

Downing Street dismissed suggestions that Britain could send a task force to Gibraltar.

"It isn't going to happen," a spokesman said.

However, he added that Lord Howard's comments underlined the strength of feeling on the issue in the UK.

"All that Lord Howard was trying to establish is the resolve that we will have to protect the rights of Gibraltar and its sovereignty," the spokesman said.

Len McCluskey, general secretary of Unite, which has thousands of members in Gibraltar, said the Government had not grasped the implications for the Rock's workers who rely on the ability to cross the border with Spain every day.

"Unite members, Gibraltar residents, Gibraltarians and EU residents all cross the border between Spain and the Rock every day, keeping the local economy strong.

"The people of the Rock don't want sabre-rattling and warmongering by some on the right of the Conservative Party.

"What they want to be told, now and in clear terms, is that they will not be used as bargaining chips in some bigger diplomatic game," he said.