How much longer can the Armed Forces go on fighting two wars at the same time? The Government faces a dilemma. For political reasons it is impossible for ministers to revert to the original plan to reduce the troops in Iraq from 4,000 to 2,500 this year; and in Afghanistan the figures have been rising steadily, from 3,300 in 2006 to 7,800 today and more than 8,000 by the end of the year.

Gordon Brown is due to make a statement to the Commons on Iraq before the parliamentary summer recess but there will be no promises on troop cuts.

The sense of foreboding within the Armed Forces is spreading. As one senior defence source told The Times, the bottom line is that “if these two campaigns continue on this scale, it could break the Army”.

The source, who was intimately involved in planning the campaigns in Iraq and Afghanistan, added: “The original design was to draw down in Iraq in order to build up in Afghanistan. This was at the heart of the strategy but it simply hasn't happened, which is why the Forces are overstretched, not so much on the bayonets [combat troops] side but in all the support areas, such as engineers and signals and logistics.”

The latest influential figure to cast doubt on the ability of the Services to carry on as they are in Iraq and Afghanistan was Air Chief Marshal Sir Jock Stirrup, the Chief of the Defence Staff, who warned the Government last month: “We are not structured or resourced to do two of these things on this scale on an enduring basis but we have been doing it on an enduring basis for years. Until we get to the stage when one of them comes down to small-scale, we will be stretched beyond the capabilities we have.”

In December 2006, in an interview with The Times, Des Browne, the Defence Secretary, also admitted that the Armed Forces were not configured or resourced for maintaining two medium-scale operations over a long period. He even suggested that the Army might have to increase in size. Yesterday officials close to Mr Browne insisted that he still felt that the two operations were “do-able”, while acknowledging that the Services were stretched.

Britain has been at war in some form, including the long-running counter-insurgency campaign in Northern Ireland, every year for the past 39 years. However, the intensity of the Iraq and Afghanistan campaigns, running simultaneously, has created unique pressures for the Armed Forces, especially at a time when all three Services have been significantly reduced in size.

So how much longer can this tempo of operations continue? The officials said they believed that “within the next 12 months” there would be a real difference in the size of the British force in Iraq. However, the last time the Prime Minister tried to cut the troop numbers by about half, to 2,500, force of circumstances compelled him to change his mind.

In March the Iraqi Prime Minister decided off his own bat to take on the Shia militia in Basra and sent Iraqi soldiers backed by about 900 US combat troops to do the job, largely ignoring the British contingent. As a result, Mr Brown called off the troop-reduction plan and British troops went back into Basra city for the first time since they withdrew in September last year. The state of play today is that although relative calm has returned to the city, security is still reliant on having armed troops on guard at key points.

A Ministry of Defence official admitted that it was going to be difficult for the foreseeable future for Mr Brown to contemplate announcing troop cuts in Iraq to ease the strain on the Army. President Bush made the same point in a different way when he spoke to the Prime Minister in 10 Downing Street last month.

Under the Government's strategy for the Armed Forces, the maximum operational commitment is supposed to be one medium-scale “enduring” campaign and one small-scale enduring operation, to run concurrently, or one medium long-term mission with one medium short-term one.

“What we've got is two medium-scale enduring operations, and that was not planned for when the MoD drew up its strategy for the Forces,” a defence source said.

Looking at the arithmetic, General Sir Mike Jackson, the former head of the Army, said that in order for regiments to have 24 months in between operational tours - the aim of the MoD under so-called “harmony guidelines” - there needed to be 60,000 deployable troops to sustain the 12,000 serving in Iraq and Afghanistan.

However, according to figures given to Patrick Mercer, Tory MP for Newark and former commanding officer of the Worcestershire and Sherwood Foresters, more than 10,000 soldiers are classed as unfit for frontline duty, reducing the number of deployable troops from the British field army to about 50,000. There is also a deficit of about 5,000 regular soldiers because of a manning crisis.

This, Mr Mercer says, makes a tipping point for the Army likely within the next two or three operational cycles. As those stretched to breaking point by the cycle of tours of duty will not need telling, this translates as a crisis looming in as little as a year to 18 months.

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