Britain is sending warships to Gibraltar after David Cameron failed in his attempt to end the diplomatic row with Spain.

A Royal Navy rapid-reaction force including aircraft carrier HMS Illustrious and two frigates will sail for the Mediterranean on Monday for a four-month deployment.

And three ships, including the frigate HMS Westminster, are to stop off at the Rock.

The 10-vessel Med visit follows weeks of rising diplomatic tension as the Madrid government holds up traffic at the border in retaliation for Gibraltar’s efforts to stop Spanish trawlers plundering fish stocks.

The Rock’s chief minister Fabian Picardo today told of his “delight” after having urged Mr Cameron to send gunboats to prove the UK is serious about standing up to Madrid.

“Gibraltar has a long, close relationship with the Royal Navy and we will be delighted to welcome HMS Westminster and the support ships back to the Rock,” he said.

“It is further proof, if any were needed, of the continuing strategic importance of Gibraltar and its territorial waters.”

Navy chiefs insisted the port stop was part of a long-planned exercise – code-named Cougar 13 – and not in response to the diplomatic row.

But it was announced the day after Mr Cameron’s personal intervention failed to end the dispute.

The PM, in a phone call to his Spanish counterpart Mariano Rajoy, issued a coded warning of legal action over the border checks and the threat to impose a £43 crossing fee.

But the checks still happened today and the Spanish hit back by criticising the Gibraltar government for making an artificial reef to protect fish stocks.

Amphibious assault vessel HMS Bulwark is the flagship of a four-strong Navy warship force backed by six Royal Fleet Auxiliary vessels.

The Response Force Task Group – with thousands of sailors and Royal Marines – will sail through the Mediterranean and on to the Gulf and the Horn of Africa, holding joint exercises with other navies along the way.

The Ministry of Defence said the annual Cougar deployment is “long-planned and well-established”.

It added: “Gibraltar is a strategic base for UK defence and, as such, Royal Navy ships visit its waters throughout the year as part of a range of regular and routine deployments.

“Elements of last year’s Cougar 12 deployment visited Gibraltar and the forthcoming visit by ships making up Cougar 13 – including HMS Westminster and two Royal Fleet Auxiliary ships – is business as usual.

“At the same time, other elements of the Task Force will be visiting Spanish ports as part of this year’s exercises.

“The same phase of the deployment will also see port visits in Portugal and right throughout the Mediterranean to Turkey and Malta before onward transit to the Middle East.”

Sending gunboats to Gibraltar harks back to a simpler age of diplomacy, when a show of Naval force was Lord Palmerston’s answer to most international ills.

We have moved on since 1850, when he ran the Foreign Office and Britain ruled the waves.

But the sight of HMS Westminster docking at the Rock sends an unmistakable message to Madrid – that as long as the residents want, the Rock will remain British.

The row over fishing rights is just a red herring as Spain is essentially testing Britain’s resolve.

So regular shows of strength by our Navy are both a morale boost for Gibraltarians – and a timely reminder to Madrid that we will not see them bullied.

Gibraltar is an outpost of Britishness at the mouth of the Mediterranean, and has been for 300 years.

The 2.3 square miles land mass, dominated by the 1,300-foot limestone Rock of Gibraltar, is one of the last remaining parts of the empire.

An important naval base up to and including during the Second World War, it has withstood many attempts to wrest it from our control.

The 30,000 inhabitants of the British Overseas Territory cling to their UK roots.

Sterling currency, red post boxes, familiar British shops and banks and the use of the English language are all legacies of the Rock's long association with Britain.

It is also represented by British MEPs in European elections, being counted as part of the South West England constituency.

The results of several referendums in Gibraltar over the years, the most recent in 2002, have been overwhelmingly in favour of remaining linked to Britain.

Captured from the Moors by the Spanish in 1462, Gibraltar was captured in turn by the Royal Navy in 1704.

Nine years later it was officially handed over to Britain in the Treaty of Utrecht, and it has remained in British hands ever since.

It is this treaty which is at the heart of Spain's claim to the land.

The Rock was ceded to Britain "to be held and enjoyed absolutely, with all manner of right for ever, without any exception or impediment whatsoever''.

But successive Spanish governments have argued that this is an anachronism and that Spain's territorial integrity justifies the return of Gibraltar to Spanish control.

Critics of Spain's attitude towards Gibraltar have pointed out that it has its own city enclaves, Ceuta and Melilla, on the north African coast, bordering Morocco.

Despite repeated demands by Morocco that the cities should be returned to its territory, Spain refuses to do so.

A new skirmish occurred with Spain in 1967 when the fascist Spanish leader General Franco began laying siege to the peninsula.

By 1969, the frontier between Gibraltar and Spain was closed to all traffic and pedestrians. After 16 years, the frontier was reopened in 1985.

The long running dispute, however, remains a headache for the inhabitants and politicians, and still causing irritations such as delays at the frontier where the Spaniards deliberately create long queues of traffic.

Other measures designed to cause a nuisance - and which have led to rebukes from British politicians - include Spanish police and Guardia Civil boats straying into Gibraltan waters.

In June David Cameron protested to his Spanish counterpart Mariano Rajoy during a Brussels summit after shots were fired at a jet-skier.

The "illegal incursion" saw a Guardia Civil boat pursued Dale Villa while he was on his jet-ski near West Beach.

Witnesses reported seeing a large number of plastic batons being fired from the vessel and splashing into the water. No-one was injured.