A Spanish navy gunboat has been accused of an "illegal incursion" into British waters off the coast of Gibraltar amid growing tensions over the territory in the lead up to Brexit.

The Infanta Cristina entered the UK waters at around lunchtime on 4 April, the Gibraltar government claimed.

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Officials said the incident – the seventh of its kind this year – saw the Royal Navy's HMS Scimitar challenge the vessel, prompting it to leave the area.

A spokesman for the Gibraltar government told The Telegraph: "Today's illegal incursion by a Spanish naval vessel is a timely demonstration of the way in which Spain routinely conducts itself in breach of the UN Convention on the Law of the Sea."

It comes the day after Spain's foreign affairs minister Alfonso Dastis called for calm from the UK following suggestions from former Tory party leader Michael Howard that Theresa May could be prepared to go to war over Gibraltar's sovereignty.

The future of the strategically important territory has spiralled into a major dispute since EU draft negotiating guidelines for Brexit said any agreement on Gibraltar would have to be run past Spain.

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The Spanish naval boat Infanta Cristina as it allegedly trespassed in British waters off the coast of Gibraltar HM Government of Gibraltar

The guidelines, published on Friday (31 March), said: "After the United Kingdom leaves the Union, no agreement between the EU and the United Kingdom may apply to the territory of Gibraltar without the agreement between the Kingdom of Spain and the United Kingdom."

Spain has long disputed British sovereignty over the land, which has been held by the UK since 1713 and currently has the status of a British overseas territory.

Gibraltar's chief minister Fabian Picardo called on the draft guidelines to be removed, saying the territory's 30,000 residents would not "tolerate being a bargaining chip or a victim" for Brexit negotiations.

Lord Howard went on to cause controversy when he likened the dispute to the 1982 war over the Falklands Islands, launched under Margaret Thatcher following an invasion by Argentina.

He told Sky News: "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."

Howard later denied he was suggesting Britain should go to war with Spain, but said he can see "no harm" in reminding the EU "what kind of people we are" during Brexit negotiations.

On 3 April, May laughed off suggestions of a war with Spain, saying: "What we are doing, with all EU countries in the EU is sitting down and talking to them.

"We're going to be talking to them about getting the best possible deal for the UK and for those countries – Spain included."

Gibraltar is a self-governing territory in all matters except foreign policy and defence, which are dealt with by the UK government.

A 2002 referendum saw its residents vote 99% against Spain sharing sovereignty with Britain, with an 88% turnout.

But last year's Brexit referendum saw them vote to remain in the EU by 96%, with an 84% turnout.

UK Foreign Secretary Boris Johnson insisted there will be no change to Gibraltar's sovereignty without consent.

He said: "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."