Downing Street today rejected Argentine claims that Britain is creating a risk to international security by "militarising" the long-running dispute over the Falkland Islands.

President Cristina Fernandez de Kirchner has said Argentina will make a formal complaint to the United Nations over the UK's decision to send one of its most modern warships and the Duke of Cambridge to the South Atlantic.

But No 10 said the despatch of destroyer HMS Dauntless to the Falklands to replace the frigate HMS Montrose did not amount to an escalation of military activity.

"We are not militarising the South Atlantic," said a Downing Street spokeswoman.

"Our defensive posture in the Falklands remains the same."

The spokeswoman confirmed that the Government has contingency plans in case of aggressive actions towards the self-governing British overseas territory.

But she stressed that the contingency plans have been in place for some time, and are not a response to the recent spike in tension between London and Buenos Aires as the 30th anniversary of the war for the islands approaches.

Ms Kirchner's comments are the latest in a series of very public displays of anger from Buenos Aires over development surrounding the disputed archipelago.

Last week William began a six-week posting in the region in his role as an RAF search and rescue pilot.

His deployment came after the Government confirmed it was sending Dauntless, one of its newest Type 45 destroyers, to the South Atlantic.

The warship is due to set sail for the region on her maiden mission in the coming months to replace the Montrose in a handover of responsibility described as "entirely routine" by Foreign Secretary William Hague.

It has also been reported that the Royal Navy is sending a nuclear submarine to the region to protect the islands from possible Argentinian military action. This has not been confirmed by the Ministry of Defence.

Speaking to an audience including Falkland war veterans and other politicians at Argentina's presidential residence last night, Ms Kirchner it was difficult to see how "the sending of an immense and modern destroyer accompanied by the royal heir who we would have liked to see in civilian clothes and not in military uniform" was not a show of purposeful military strength by the UK.

She said: "I have instructed our chancellor to present formally to the Security Council of the United Nations and before the General Assembly of the United Nations this militarisation of the South Atlantic which implies a great risk for international security."

Argentina would be opposing "this militarisation of the South Atlantic" because it was a region where "peace reigns", said Ms Kirchner.

Speaking to reporters at a daily Westminster briefing today, the Downing Street spokeswoman said it was a matter for Argentina what issues it wished to raise at the UN.

She said: "The people of the Falklands choose to be British. Their right to self-determination is a principle enshrined in the UN charter.

"The Falklands are already discussed by a UN committee and it is up to the Argentines to decide whether they are going to raise it at the UN.

"The fact is that one of the key principles of the UN charter is self-determination and that is what we are talking about in relation to the Falkland Islands."

There was "no suggestion" that Britain needs to increase its military presence or its defence assets in the South Atlantic, said the spokesman.

Asked if the Government had plans in place to deal with any aggression against the Falklands, she replied: "Yes, we have contingency plans. You would expect the Government to have contingency plans."

But asked if these plans were new, she said: "No. The contingency plans have always been in place."

The Foreign Office made clear that the UK will not enter into negotiations over the sovereignty of the islands, which have been in British hands since 1833 and are known to the Argentinians as Las Malvinas.

A Foreign Office spokesman said: "The people of the Falkland Islands are British out of choice. They are free to determine their own future and there will be no negotiations with Argentina over sovereignty unless the islanders wish it."

Relations between London and Buenos Aires have been increasingly frosty in the run-up to the anniversary of the Argentine invasion on April 2 1982.

In December, Prime Minister David Cameron accused the Buenos Aires administration of "colonialism" after the Mercosur grouping of countries, which includes Argentina, Uruguay, Brazil and Paraguay, announced that it would ban ships sailing under the Falkland Islands flag from docking at their ports.

Interest in the islands has been heightened by recent progress in the drive to exploit oil and gas reserves under the seas off their shores.

Ms Kirchner denied last night she was beating the drum for war.

"We are people who have suffered too much violence in our country. We are not attracted to armed games, or wars, on the contrary," she said.

"No land, no place can be a spoil of war. We do not believe in the spoils of war."

She also made clear her view that the British are occupying the Falklands, saying: "It is an anachronism that in the 21st Century that there are still colonies: there are only 16 cases (of colonisation) in the whole world, 10 of them are English."

Towards the end of her speech she made a direct plea to Mr Cameron, saying: "I want to simply ask the English Prime Minister that he gives peace a chance, that some time he gives peace a chance."

British Falklands veteran Simon Weston, who was badly injured during the conflict, described the Argentinian president as "a troubled woman".

He told the BBC: "I don't know what she thinks she is going to gain by annoying everyone with these continuing arguments.

"Ultimately, what are the UN going to do? Are they going to sign a sanction against Britain? I doubt it very much."