The Ministry of Defence has released first details of the large scale operation over Christmas that cost five British soldiers' lives.

It has emerged that UK forces in Afghanistan battled the Taliban at close quarters, knee deep in mud in fighting reminiscent of the First World War.

Operation Dagger's aim was to assault four key enemy bases. The insurgents were threatening Lashkar Gah, Helmand's provincial capital that had come under attack in the autumn.

Involving 1,500 Nato and Afghan troops, it was the Royal Marines' biggest deployment so far in Afghanistan.

In highly-mobile combat, the green berets had to "yomp" as much as 35 miles to seek out their enemy.

The operation began on December 7 when ground troops, backed by Danish Leopard tanks, began assaulting enemy positions near Nad-e-Ali, about five miles northwest of Lashkar Gah.

After a pause of three days - out of respect for the Muslim festival of Eid - the Marines finally secured their objective by fighting from ditch to ditch in heavy rain and clinging mud.

"Almost every day involved intense fire-fights, ranging from rocket-propelled grenades and small arms shoot and scoots to four-hour battles with the enemy as close as 30 metres," said Captain Dave Glendenning.

An engineer corporal described conditions: "At times we were constructing in torrential rain with mud up to our knees. Whenever the enemy saw us they would have a go. There were a couple of close calls."

What one commander described as a "canny and determined" foe, put up a further fight after withdrawing to two neighbouring villages.

The fiercest resistance was at Zarghun Kalay where hand-to-hand fighting broke out as the Taliban tried unsuccesfully to surround and cut off the British.

The two-day battle claimed the life of 21 year old Rifleman Stuart Nash.

The other UK fatalities were Cpl Robert Deering, 33, Lance Corporal Ben Whatley, aged 20 and Marines Tony Evans, 20, and Georgie Sparks, 19.

About 100 Taliban, among them a senior commander, are claimed to have been killed.