Michael Howard’s suggestion that Britain might go to war over Gibraltar has been dismissed by a defence expert as both “hilarious” and completely unrealistic.

Peter Felstead, editor of Jane’s Defence Weekly, told The Independent that however tense Brexit negotiations got, Britain and Spain going to war over Gibraltar was something “that is just not going to happen”.

“We are talking about two Nato allies,” he said. “There are occasional differences between allies, but this would never be allowed to blow up into anything that would constitute open conflict.”

“It’s quite hilarious,” he added. “I would say it’s a very bolshy way to talk to a Nato ally, and not very helpful.”

His comments came as the Spanish government suggested that Britain should calm down and regain its “traditional composure”, and as former Labour Foreign Secretary Jack Straw dismissed Tory ex-leader Lord Howard’s idea of war over Gibraltar as “absurd 19th-century jingoism”.

Invoking the spirit of Margaret Thatcher during the Falklands War, Lord Howard told Sky News 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.”

Downing Street has now sought to defend Lord Howard, saying all the Conservative grandee was doing was trying to establish "the resolve" that Theresa May's administration has to defend the sovereignty of the territory in negotiations with the EU over Brexit.

Mr Felstead, however, pointed out that no two Nato countries have ever fought a war with each other, “and in Nato you have allies who have in the past been much more belligerent to each other – I am thinking of Greece and Turkey.

“Nato has managed to stop Greece and Turkey engaging in open conflict for many decades, so I don’t think it would be a problem for them to stop the UK and Spain.”

The nearest two Nato allies got to war, he said, was in 1974 when Turkey invaded northern Cyprus, an island with a large Greek population, but nonetheless independent from Greece.

“Gibraltar,” Mr Felstead added, “Is not the same situation. For a start, it’s not an island. It’s right along the coast from where many Brits will have experienced going on holiday.

“And from a military point of view it’s also a key strategic listening post in the Mediterranean for the UK and Nato as a whole, so Nato certainly wouldn’t want a war over that bit of territory.”

35th anniversary of Argentine invasion of the Falklands

As a retired Rear-Admiral told the Telegraph that Britain could “still singe the King of Spain’s beard”, but the Government had to invest “appropriately” in military hardware if it wanted to “talk big” over Gibraltar, Mr Felstead said the Falklands comparison was at least interesting in one respect.

“If the Argentinians had waited to make their move and not been so impatient because of their own political situation, they would have been much more successful, because in 1982 we were planning to can our aircraft carriers: within months or a year we wouldn’t have had them for that operation.

“Of course at the moment, we don’t have any aircraft carriers. We will soon have the largest warships the UK has ever produced, the aircraft carriers HMS Queen Elizabeth and HMS Prince of Wales, but they are still being built.

“And we are not yet actually at the point where we are training up our pilots on the F-35 joint strike fighters that will go on the carriers. The RAF is just at the stage where it has prepared the flight simulators to start training our pilots.”

Mr Felstead stressed, however, that he was not suggesting that this was Spain’s golden opportunity to have a go at retaking Gibraltar, because in the – totally improbable – event of such a war, aircraft carrier capability would be irrelevant.

“If we really wanted to do something, we have got RAF Akrotiri in Cyprus, and there would be no problem flying from the UK because it is closer, and you could refuel in the air to give you more time over the target.”

Nor, he added, should military chiefs worry about the significant reduction in size of the Royal Navy since the Falklands War. By comparison, Spain decommissioned its only aircraft carrier the Principe de Asturias in 2013:

“You would have to say we have stronger armed forces because we spend more. The Spanish have gradually been spending more on their armed forces, but only after quite significant cuts.

“They are solid Nato ally, but not one of the stronger European Nato allies.”

In previous military confrontations over Gibraltar, Spain has tended to come out second best. Britain captured the Rock in 1704 during the War of Spanish Succession, when an Anglo-Dutch fleet under the command of Admiral George Rooke conducted a five-hour, 15,000-cannon bombardment followed by a weakly opposed landing.

The 1713 Treaty of Utrecht ending the war stated that "the town, castle and fortifications [of Gibraltar] were to be held and enjoyed for ever without any exception or impediment whatsoever."

But in June 1779, with Britain distracted by the American War of Independence, Spain allied with France and tried to reclaim the Rock, leading to what became known as the Great Siege of Gibraltar.

Lasting three years and seven months, until February 1783, it became the longest siege endured by British Armed Forces.

The British suffered so severely from lack of food that at the siege’s height that the Governor, General George Augustus Eliott, felt compelled to live on 4 ounces of rice a day as an example to his troops.

They had at most 7,000 men and only 96 guns, against more than 30,000 French and Spanish sailors and marines, and more than 200 guns.

But when the “Grand Assault” came in September 1782, the tens of thousands of Spanish spectators who had gathered on the surrounding hills in anticipation of victory were disappointed. The British responded with red-hot shot which blew up three floating gun batteries. Seven other batteries were so badly damaged that the Spanish had to scuttle them. The Spanish and French suffered more than 700 casualties.

Mr Felstead, however, said that Lord Howard probably shouldn’t expect any rematch to follow the same lines, because the nature of conflict is changing so much.

He said: “If you look at what Russia did in Crimea, you are no longer talking about state against state. You now have hybrid warfare: cyber warfare, disinformation, people patrolling the streets – the little green men – armed to the teeth but with no insignia on their uniforms, and then it turns out they are Russians and the place is annexed.

“It wouldn’t necessarily be that Spain would do the same thing, but it wouldn’t look like open conflict.

“We would reassert our sovereignty with patrol boats, there would perhaps be welling up of sentiments among local populaces in support of one way or another.