The government is expected to announce the deployment of reinforcements for Afghanistan this week ahead of a renewed Taliban spring offensive against British troops in the country's southern provinces, The Herald can reveal.

But military sources say the number sent will be less than half of what successive commanders have requested, since only one battalion of between 500 and 600 Cyprus-based soldiers is available as a ready-reserve for both Iraq and the undermanned garrison in Helmand.

As reported exclusively by The Herald last week, pressure has been growing on the government to add a battlegroup of 1200 to the 4000-strong garrison in Afghanistan to allow tactical flexibility in countering the Taliban across Helmand, an area four times the size of Wales.

At the moment, fewer than one in four of the troops in the province are being used in a combat role, partially because there are only eight Chinook transport helicopters to move them rapidly across vast distances.

The six Chinooks committed originally were reinforced by two more last year. One of those had to be withdrawn from the Falklands and the other from squadron training duties in England.

Six of the Army's eight deployable combat brigades are currently tied up on operations, recovering from tours of duty or training to replace those on the frontline.

The other two brigades are catching up on training for their primary war-fighting roles rather than counter-insurgency campaigns or taking part in trials of the Army's troubled Bowman battlefield digital communications' system.

A military source told The Herald: "The government is about to announce reinforcements but, while it will be welcome, it is a token gesture. The numbers are just not there. Even if they were, the helicopters vital to operations in that terrain over those distances are not available.

"The Taliban are likely to unleash a series of major attacks in Helmand and Kandahar when local spring arrives at the end of February.

"But it's likely they learned a lot of lessons from the battering they took at the hands of the Paras last year. We will see more roadside bombs and suicide attacks. They are not stupid. They know how short we are of helicopters, even if our own government doesn't appear to."

US Army Lt Gen Karl Eikenberry, outgoing commander of Combined Forces Command Afghanistan, said he expects the Taliban to launch a terror offensive in the south and east of the country.

"I would expect that the enemy will have its main effort against southern Afghanistan," he said.

"The enemy will try to conduct terror attacks against Kandahar and other urban centres. They will also try to restrict the mobility of Nato forces and to conduct attacks against district centres or outlying areas at night."

A leaked British Army internal briefing paper admitted last week that "insufficient" troops had been sent to fight the Taliban.

Reports from Helmand yesterday claimed that, despite Prime Minister Tony Blair's promise last year that commanders would be supplied with "everything they need to get the job done", dozens of urgent requests for equipment had been turned down on cost grounds.

Troops serving in Helmand say all four of the specially-protected vehicles used to extract casualties from unmarked minefields have broken down and there are shortages of night-vision goggles.