Spain has been accused of an act of war after one of its gunboats was chased out of British waters off Gibraltar amid rising tensions over the peninsula in the lead up to Brexit.

The Infanta Christina ship sailed past the coast of the British territory at around lunchtime in what Gibraltar said was an illegal incursion and was pursued by a British naval vessel patrolling the Rock until it left.

The armed ship sailed into British waters just hours after Spanish foreign minister Alfonso Dastis told Britain to 'calm down' following Lord Howard's suggestion Theresa May would go to war over Gibraltar.

This image was taken off the coats of Gibraltar earlier today. The Spanish ship, pictured right flying the Spanish flag, made incursions into British waters where it was followed by HMS Scimitar (left)

The ship was around a mile off the coast of Gibraltar, a witness who lived on the said

British ship HMS Scimitar (left) tailing the Spanish Patrol Boat P77 Infanta Christina (right)

The government of Gibraltar posted a video of the ship on Twitter and wrote: 'Illegal incursion into British Gibraltar Territorial Waters by Spanish Navy patrol ship Infanta Cristina this afternoon.'

Tweeting a picture of the ship that he took today, David Parody wrote: 'In true Spanish style, to calm down, they send us a gun boat!'

Mr Parody, a Gibraltarian who was born and lives there, said the ship was around a mile off the coast, and claimed it is the seventh incursion into British waters by Spanish ships this year.

Asked if Britain should take military action, he said: 'We don't want to see gun boat diplomacy because there would be no winner in that, but this is bullying.

'We live in an age of diplomacy and Spain should respect that. Britain has even offered to take Spain to international court to resolve this issue and Spain has refused.'

The path of the British HMS Scimitar, which followed the Spanish vessel today, reveals how it had sailed well within Gibraltarian waters.

Colonel Bob Stewart, a former senior British military commander and Tory MP, said: ‘I have raised before the number of incursions by Spanish naval vessels and said they are deliberately sending their ships into the territorial waters of another state without permission.

‘This could, at the very least, be deemed a very hostile act. It could be an act of war. Spain is deliberately stoking up the situation.’

The red line shows the path of the HMS Scimitar, which pursued the Spanish ship today. The purple line marks the end of Gibraltarian waters

Mr Parody claims that there have been more than 100 incursions into British waters by Spanish navy ships since 2014, and even aircraft have also flown in Gibraltarian airspace without permission.

The vessel's appearance today comes after Lord Howard said Britain should be ready to go to war over Gibraltar, which MPs have warned will be used as Brexit leverage by Spain.

A Spanish Ministry of Foreign Affairs official said the Infanta Cristina was conducting a routine patrol to monitor migration or drug trafficking across the Gibraltar Strait.

Mr Parody added: 'The Spanish are claiming this is a matter of routine but to do it hours after Lord Howard says Britain would be willing to go to war is obviously to send a message.'

A spokesperson for HM Government of Gibraltar said: ‘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 is almost as if Lord Howard has unnerved someone senior in the Spanish Navy’.

This week's war of words comes after years of disagreements between Britain and Spain over the peninsula off the Spanish coast, which has been a British overseas territory since the 18th century.

Its 30,000 resident overwhelmingly rejected Spanish sovereignty in two referendums in 1967 and 2002, but Brexit raised new questions after they voted to stay in the European Union in June.

But Mr Parody says Spain needs to respect their international waters as the constant incursions are making residents feel nervous.

'If there were armed paramilitary vehicles arriving in London every day, people wouldn't feel secure,' Mr Parody added.

This graphic shows how the Spanish vessel entered British waters before being intercepted

The Spanish Patrol Boat P77 Infanta Christina which sailed into Gibraltar's territory today

It comes just hours after Spain told Britain to 'calm down' and demanded that Gibraltar (pictured) be returned to them once Britain leaves the EU

A file photo of the HMS Scimitar, which has seen off the Spanish ship that ventured illegally into Gibraltar's territory

Theresa May yesterday played down the threat of military conflict over Gibraltar yesterday.

Former Tory leader Michael Howard had suggested she was prepared to show the 'same resolve' defending the Rock as Margaret Thatcher had over the Falklands

The EU has said Madrid would have a veto over Gibraltar's inclusion in any post-Brexit trade deal but yesterday Mrs May dismissed the idea of going to war with a Nato ally.

Asked whether, in Winston Churchill's famous phrase, it would be 'jaw-jaw, not war-war', Mrs May said: 'What we're doing with all European countries in the European Union 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. It's definitely jaw-jaw.'

Mrs May also rejected suggestions that Gibraltar had been hung out to dry by her failure to mention the fate of the Rock in her letter to the EU setting out her Brexit negotiating position last week.

Gibraltar's Chief Minister Fabian Picardo said Spain was trying to bully Gibraltar and that the EU was allowing the bullying to happen

'I spoke to the chief minister of Gibraltar yesterday. What we are going to be doing is continuing to support Gibraltar – our position on Gibraltar has not changed,' she said.

'We will be working with them as part of our negotiations to get the best possible trade deal for the UK and the best possible deal for Gibraltar.

'Our position on the sovereignty of Gibraltar has not changed and will not change.'

Spain's foreign minister yesterday mocked how tensions had quickly escalated since the EU published its draft Brexit negotiating guidelines on Friday and called for Britain to calm down.

Ahead of a meeting with Brexit Secretary David Davis in Madrid, 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.'

Meanwhile, Gibraltar's chief minister Fabian Picardo attacked European Council president Donald Tusk.

'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 ,' he said.

Mr Picardo said Spain was trying to bully Gibraltar and that the EU was allowing the bullying to happen.

But the European Union's Brexit negotiator was today refusing to be drawn into a row over the future of Gibraltar as Britain moves forward with its divorce from the bloc.

Asked whether Brexit negotiations launched last week are off to bad start due to the dispute about the British territory, Michel Barnier said Tuesday 'keep calm and negotiate.'

Pushed to comment, Barnier said 'juridically speaking, Gibraltar will exit the Union at the same time as the United Kingdom.'

The rocky enclave at the tip of the Iberian peninsula has been a British territory - and cause of friction between the U.K. and Spain - since 1713.

The latest spat arose from the EU's Brexit negotiating guidelines which leave Britain and Spain to thrash out what agreements will apply to Gibraltar.