Spain continues to play a dangerous game, now HMS Westminster has entered the harbor of the enclave a routine exercise, Downing Street says.

The Royal Navy warship sailed in as tensions between Spain and the British territory were described as their worst for 40 years.

The type 23 frigate, which left Portsmouth naval base six days ago, is due to spend three days on the Rock, before joining several other vessels taking part in a pre-planned international training exercise called Cougar 13 in the Mediterranean and Gulf.

Its visit was described by the Ministry of Defence as “long-planned”.

But Sky’s Defence Correspondent David Bowden, in Gibraltar, said given the growing diplomatic spat, the warship’s presence will be seen as a “strong symbol” of Britain’s desire to defend its territory.

Yesterday, a flotilla of more than 30 fishing boats was “corralled” by Royal Navy vessels after protesting near the spot where Gibraltar’s government placed 70 concrete blocks in disputed waters next to the Rock.

Gibraltar says it has created the concrete artificial reef there to protect local fish stocks from trawling, but Madrid says it restricts their right to fish.

The Spanish government has accused Gibraltar of laying the blocks “without the necessary authorisation” in “waters that are not theirs”.

It responded by introducing additional checks at the fenced border, and suggesting a 50 euro (£43.30) fee could be imposed on every vehicle entering or leaving Gibraltar.

Yesterday’s protest prompted calls for renewed efforts from the European Union to solve the dispute.

Julie Girling, a Conservative MEP for Gibraltar, called the flotilla a “provocative attempt to stir things up yet again” by a government in Madrid facing allegations of corruption.

Afterwards, Fabian Picardo, Gibraltar’s chief minister, thanked the British authorities for their help.

Mr Picardo, who has reportedly received death threats and been targeted by Spanish internet trolls, wrote on Twitter: “Big thank you also to Royal Navy, Gib Defence Police, HM Customs and Port Authority for their deployment too.

“Cool, professional and calm!”

He said “hell will freeze over” before Gibraltar removes the concrete reef and accused Spain of behaving like North Korea.

Spain’s Prime Minister Mariano Rajoy says he will take all legal measures to defend his country’s interests.

Locals waving Union flags gathered on the quayside to watch HMS Westminster come in.

Andrea Jones, 46, who works for an online gaming company and has lived in Gibraltar for 12 years, said the frigate’s arrival was “a two-fingered salute towards Spain”.

Retired Royal Gibraltar Police officer Michael Sanchez, 53, said he would like to see British warships off Gibraltar more often.

“It is getting to be out of control, it is not a spat any more,” he said. “If you park something out there grey (a warship) for a couple of days you can see them (the Spanish) calm down.

He added: “These guys need to be taught a lesson. It is no good having (William) Hague, (David) Cameron sending protests galore.

“You have got to stick your nose in there, your face into their face. If not they just get away with it.”

On Friday, Prime Minister David Cameron raised the dispute with European Commission president Jose Manuel Barroso.

He said the checks – which have seen huge delays at the border in recent weeks – were “politically motivated and disproportionate” and therefore contrary to the EU right of free movement.

The row has set relations between Spain and the territory back 40 years, according to Edward Macquisten, chief executive of the Gibraltar Chamber of Commerce.

He said it was also having an impact on Gibraltar’s high season tourist trade, which usually sees hordes of British visitors from Spanish resorts.

Spain ceded sovereignty of Gibraltar to Britain in 1713, but has persistently sought to regain the tiny enclave.

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