British forces were caught up in a ferocious gun battle in southern Afghanistan yesterday after a Taliban ambush in a cornfield.

Two soldiers were taken to hospital by helicopter for emergency surgery - one with very serious injuries - when insurgents opened fire with machine guns and Rocket Propelled Grenades (RPGs) just yards away.

Minutes beforehand, the troops from the 1st Battalion the Worcestershire and Sherwood Foresters Regiment (1WFR) had been standing in a suspected Taliban compound in noman's-land deep inside Helmand Province's notorious Green Zone.

Its occupants had apparently left, leaving behind only a few daily provisions, a cache of rocket flares and a framed photograph of a Jihadist fighter posing with an AK47.

But as a platoon from the regiment's B Company made their way into the adjoining field - creeping along a perimeter ditch, out of sight behind ripening corn, the Taliban were lying in wait.

It was to be their 28th "contact" and fourth ambush in four months.

They were among British forces taking part in a fresh push against the Taliban front line codenamed Operation "Naiza" - meaning spike - inside the Green Zone, a lush streak of land cutting through the desert where the insurgents have taken refuge. The operation began late on Monday night with scores of soldiers patrolling across the Green Zone in darkness to a fortress-like outpost held by 1WFR troops throughout the summer.

Setting out after first light yesterday, the troops had stormed a maze of mud-walled compounds suspected of harbouring Taliban before entering the field to search for a better vantage point.

Suddenly, pinned down in a ditch as gunfire cracked overhead, the soldiers' training immediately kicked in, coolly returning fire with the first of hundreds of rounds before taking cover from incoming RPGs.

Troops behind the ditch immediately began shouting out each other's names to account for their comrades but within less than a minute the call was repeated down the line: "We've got one casualty, we've got one casualty."

Crawling on their stomachs, they escaped along the shallow ditch towards a deeper trench as others returned fire. But as they entered the second ditch Taliban fighters had made their way along behind a hedge into the first compound, threatening to outflank and surround them. Mortar specialists put down a smoke blanket as a RPG smashed into a tree just feet away from one of them.

Meanwhile the infantrymen crawled down a thorn-filled trench, taking refuge behind a mud wall 100m from the Taliban and opened fire with machine guns.

With reinforcements from another platoon providing covering fire the casualties were safely evacuated.

Worst hit was a private who had been at the front of a line moving through the field when he was shot by a Taliban fighter in a brown "dish-dash" trouser suit and turban.

Corporal Clint Buchanan, 25, from Ilkeston, Derbyshire, was next to him in the line.

He said afterwards: "The guy was in the corner as he attacked him, he was in cover, he waited for him to get all the way up.

"My friend got hit, the bloke went back from there towards the others and obviously heard him moaning in pain because he had been shot.

"Then a couple of minutes later he just came back, casual as f*** and went to finish him off."

But the insurgent was shot by the British troops before he could get any further. The private is described as in a serious but stable condition in hospital. Another soldier was airlifted with him to Camp Bastion with a shrapnel wound to his arm and is expected to make a full recovery.

The platoon's acting second in command, Corporal Andy Geering, 36, was hit by a small piece of shrapnel in his arm, but did not need hospital treatment and was able to fight on.

He had been due to go home on leave within hours when the battle broke out.