Corporal Donald McPhee was providing “top cover” in his Mastiff armoured car when it hit the land mine. At the best of times, top cover is an exposed position. It means standing up with your head poked through the roof of the vehicle in order to man the big grenade-firing machinegun, which is the Mastiff's main weapon.

It also means taking the full force of a blast if you drive over a roadside bomb. Since February, when they began their tour of duty in Helmand, Corporal McPhee, 32, of Glasgow, and soldiers of 2 Scots (Royal Highland Fusiliers) have been patrolling the treacherous desert area northeast of the town of Musa Qala. Their task is to protect the town, to keep the Taleban at bay and to reassure locals that the British are on their side. That task is not helped by the constant threat of roadside bombs, or IEDs as they are known.

They are the Taleban's principal method of attack, and their effect can be devastating - only a week ago Lance Corporal James Johnson, 31, of 5 Scots (Argyll and Sutherland Highlanders), was killed by a bomb left behind by the Russians.

Corporal McPhee was in the second of a three-vehicle convoy when it hit a mine. The convoy had pulled up at a VP, or vulnerable point, where roadside bombs might be expected, but due to a misunderstanding, the crew of the Mastiff thought it was clear.

As the convoy drove forwards, there was an explosion, which blew a front wheel off and hurled it 40 metres. It also sucked the air out of the Mastiff, taking Corporal McPhee and his gun with him. “For a moment I couldn't see anything. Everything was black with sand and smoke, and when it cleared, I couldn't hear. I thought, I've gone deaf, then I realised the blast had ripped the cord out of the headset. I plugged it in and I was fine.”

There have been nine such explosions since the Scots took over at their Forward Observation Base, known as FOB Edinburgh, the farthest-flung of the task force's outposts in Helmand.

Jonathan Brennan, 19, of Bettyhill in Sutherland, was in a Warrior armoured vehicle when it hit a bomb. It blew the left-hand track off, but again there were no casualties. Both the Mastiff and the Warrior have sufficient armour to protect their crew. The floor of the Mastiff has been made in a V shape to divert the blast upwards and sideways.

None of this is a substitute for the basic, and now the most important, military task confronting British units in their war against the Taleban. The ferocious fort assaults of 2006 and 2007 have been replaced by the IED and the suicide bomber.

Yesterday, 2nd Lieutenant Calum Macleod, 22, platoon commander of 4Scots (The Highlanders), was supervising the patient training of his men in the art of detecting roadside bombs. Details of the technique have to remain secret, but the fact is there is, as yet, no fail-proof technology that guarantees detection.

“A lot of it comes down to instinct,” Lieutenant Macleod said. “You get to know the places that the Taleban prefer, the narrow bits in the road, where there is not much room for manoeuvre.”

I watched the painstaking process of finding a bomb. Lance Corporal Andy Naughton, 28, a territorial from Banff, had to lie face down and then inch forwards, exploring the ground with his fingers. He marked it, and orders were passed back for the bomb disposal team to blow it up.

I asked him if he had been scared. “No, not really,” he said. “In fact, you get a bit of a buzz.” This, then, is the tactic being developed in this far-flung outpost of the Helmand operation. It is a slow and laborious process - rather like the war itself.

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