More than 4900 trained soldiers voted with their feet and left the Army before their enlistments were up in the 12 months to March this year, while just 4000 raw recruits signed up to replace them, The Herald can reveal.

The numbers opting for early release from the infantry have more than doubled on a month-by-month basis from an average of between 130 and 160 in 2005-06 to an average of about 400 in 2006-07. The continuing exodus means that frontline units such as the infantry are now between 3000 and 4000 below fighting strength and continuing to haemorrhage the experienced majors, captains, sergeants and corporals they can least afford to lose.

Detailed statistics seen by The Herald show that recruitment and retention worsened by the equivalent of one and a half battalions at a time when commitments in Afghanistan are about to increase to around 8000 men and 5000 troops are still in Iraq.

The Ministry of Defence claims that accurate figures for "voluntary outflow" and manning comparisons will not be available until 2008 because of problems with a new IT system.

But The Herald has obtained a monthly breakdown of both entry and voluntary outflow exit numbers. The "VO" system was rebranded last year from its previous designation as "premature voluntary retirement".

The MoD recently launched a new recruitment drive based on television and newspaper adverts for the "One Army" concept of attracting new volunteers for both hard-pressed regular and Territorial units.

The recruitment target for 2007-08 is 13,817 and is due to increase to 14,104 in 2008-09. The Army is also seeking 652 officer cadets by next year and a further 658 by 2009.

North of the border, where the five-battalion Royal Regiment of Scotland is 313 soldiers short of full strength, the MoD has launched an £800,000 advertising campaign to bring in new recruits. More than half of the RRS is to deploy to Afghanistan in the spring as part of a major offensive to break the Taliban's hold on Helmand province.

Even the Parachute Regiment, an elite, three-battalion force which has seldom had to struggle to fill its ranks, is 274 men below its "bayonet strength". The entire regiment, plus TA reinforcements, is also to go to Afghanistan in March.

Brigadier Allan Alstead, a former commander of 51st Highland Brigade, said: "The key to recruiting is pay. It is time our servicemen were paid a wage that reflects the job they do and the dangerous conditions they have to survive in day by day."

The MoD said recruitment was "challenging" and had been "affected by a number of factors, including parental reluctance to allow their children to join the military and the availability of further educational opportunities".