A force of around 1000 soldiers will be sent to the Falkland Islands in groups of 150 to 300, to train them for a rapid deployment. The move comes as the Falklands faces its biggest threat from Argentina in nearly 20 years.

The group will include soldiers from the Royal Artillery and 3 Commando, Royal Marines, with each group staying on the islands for three to six weeks. A senior source told the Sunday Express: “The aim is to put more than 1,000 troops from five different cap badges into the islands by November but they will deploy in small groups from 150 to 300, for short tours.”

The military source claimed the plan did not represent a “permanent increase in garrison numbers but a series of high-readiness exercises”. A view that was confirmed in a statement by the Ministry of Defence.

Air Commodore Andrew Lambert, of the UK National Defence Association, claimed the overall strength of the garrison was too small. He told the paper: “I was deputy commander and air commander in 1997, when we had 2,000 troops stationed on the islands.

“At that time we said we were not prepared to reduce them because we could not know what Argentina had in mind: 2,000 troops was, in our opinion, the absolute minimum required to secure a proper defence. Yet this has been reduced to 1,200 and that includes cooks and medics.”

The training is taking place so the Islands are ready for any invasion that might come before the new aircraft carrier, HMS Queen Elizabeth, is fully operational in 2020. Until that time there are real concerns the British military could not retake the Falklands.

In recent weeks Argentina has done a deal with Russia to 12 lease supersonic bombers. This led the UK to send HMS Dragon, a Type 45 destroyer, to the South Atlantic after a deployment in Chile. The Islands will also see their air defence system upgrades but this will take at least five years, and cost £200m.

Both the Falkland Island’s Government and Whitehall are said to be worried that President Cristina Kirchner will use the dispute over sovereignty to divert attention from her own internal political problems in Argentina. She is also nearing the end of her second term of office and might be inclined to take more risks in the international arena.

An MoD spokesman said: “Throughout the year UK personnel routinely travel to the Falklands to take advantage of the excellent training opportunities the islands offer. Our military posture in the south Atlantic is appropriate and we regularly assess potential threats to ensure we retain an appropriate level of defensive capability.”