The British Army is expected to escape any major reduction to its manpower in the forthcoming Strategic Defence and Security Review (SDSR) while the war in Afghanistan continues, according to defence sources.

The National Security Council, which is in overall charge of the process, is due to meet today under the chairmanship of the Prime Minister to consider a range of options.

There has been speculation that the Army may lose up to 20,000 personnel from its strength of just over 100,000 as part of its share of savings being demanded in the review. Both the RAF and the Navy are due to face cuts in their numbers of aircraft and ships as well as personnel.

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However, it is believed that the Government is likely to ringfence the size of the Army until 2015 – by which time the British mission to Afghanistan should have ended its combat role.

The Defence Secretary, Liam Fox, was told during a recent visit to Washington of American concerns about the effect that cutbacks in the British Army may have on operations in Afghanistan. The UK contingent, of just under 10,000 troops, is the second biggest after the US force and is seen as playing a key role, especially at a time when other coalition countries, such as Canada and the Netherlands, are pulling out of the conflict.

The House of Commons Defence Select Committee stated in a recent report that the swingeing cuts of 20 per cent being demanded by the Ministry of Defence would endanger current operations.

By 2015, the number of soldiers to be laid off would be likely to be reevaluated. There is an understanding that some reductions then are inevitable as it is unlikely that whichever UK government is in power would want to embark on expeditionary warfare in the short term after the long and costly commitments in Iraq and Afghanistan.

In the meantime, Army chiefs would be prepared to accept a reduction in the amount of battlefield armour to show that it was prepared to make sacrifices in the economic climate.

Lib Dems in the Coalition Government have suggested that the issue of replacing the Trident nuclear deterrent should be left until 2015. Postponing cuts in Army numbers may lead to accusations that the Government is attempting to avoid decisions on the most controversial of the savings options.

The defence review takes place against a growing feeling in the military that the sheer scale of the cut would be a heavy blow to the efficacy of the armed forces. Defence officials are concerned that the Treasury appears to be taking a lead role.

A defence source said: "It cannot but adversely affect the reach and effectiveness of our armed forces. This process is going at almost four times the rate of the previous SDSR, it seems that it is being cost-driven and time-driven rather than being driven by strategic and security concerns."

Today's National Security Council meeting will give David Cameron an array of possible savings. Several options are likely to be prioritised but no firm decisions will be made for several weeks, according to Whitehall officials.

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