More than half of the Royal Regiment of Scotland's soldiers are on standby to go to Afghanistan next spring to take part in the biggest ground offensive since the allied invasion six years ago.

The Herald has learned that two complete battalions out of the five in the RRS, plus a reinforced armoured infantry company from a third, are scheduled for deployment in March.

It means that up to 1400 Scots soldiers will be fighting in Helmand province alongside 1500 paratroopers and several hundred special forces troopers as the spearhead of an 8000-strong UK deployment.

As revealed exclusively on Friday, the Royal Highland Fusiliers - now 2nd battalion, RRS - has already been ordered to begin training for the mission.

The Glasgow and Ayrshire soldiers will be joined by the Argyll and Sutherland Highlanders (5 RRS), who are in the helicopter assault role as a component unit of 16 Air Assault Brigade.

The Herald understands that a request has also been made for a company group from the Highlanders (4 RRS), who operate as armoured infantry using Warrior fighting vehicles.

Preliminary warning orders have already gone out to the three units, according to military insiders, and training will be stepped up over the winter.

The Argylls are based in Canterbury and the Highlanders in Fallingbostel, Germany. The RHF barracks are at Glencorse, near Edinburgh.

A regimental source said yesterday: "All of the battalions are under strength by about a company apiece and will need to backfill with individual replacements from other units. The peacetime and wartime establishments as far as numbers are concerned makes a big difference. Instead of about 105 officers and men per rifle company in barracks, they need up to 120 in combat.

"The call will go out shortly to the 6th and 7th Territorial battalions of the RRS for volunteers to augment the regulars, but most of the manpower will have to be drawn from the three other regular battalions. We call it the Rent-a-Jock system."

The RRS has 2447 officers and men in its five battalions - 313 short of its manning establishment.

Even the Parachute Regiment, all three of whose battalions will be operating together alongside the Scots next year for the first time since the Suez crisis in 1956, is 274 men short and will be plugging gaps in its ranks with Territorials.

The Paras' 1st battalion forms the core of the new Special Forces Support Group and is tasked with providing back-up and security for SAS missions.

Insiders say the SAS itself is to deploy up to three of its four "sabre" squadrons, leaving only the counter-terrorist warfare wing back in the UK, as part of the maximum effort offensive to break the Taliban's hold on Helmand province.

Prince William has, meanwhile, sent his condolences to the widow of Major Alexis Roberts, 32, who died in a roadside bomb explosion near Kandahar on Thursday.

The Gurkha Rifles officer was the prince's platoon commander during his training at Sandhurst.

His death took the number of British forces personnel to be killed in Afghanistan since the start of operations there in 2001 to 82.

Maj Roberts was also the first UK soldier to be killed in the country since September 20.

An MoD spokeswoman said yesterday: "We cannot confirm the details of military roulements until the House of Commons has been formally informed. Anything else is speculation."

The MoD confirmed on Thursday that the RHF was training for a deployment in March.