British troops in Afghanistan are to hand over responsibility for the Sangin area of Helmand province to US forces, the BBC understands.

But far from surrender, argues former head of the army General Sir Richard Dannatt, the increase in troops as US forces take over is exactly what is needed.

"We've always said we need boots on the ground, and I've always said I don't care whose feet are in those boots," he told John Humphrys.

We should never have expected the outright victory on the ground in Afghanistan, argued Professor Michael Clarke, director of the Royal United Services Institute.

"Winning in this operation is a score-draw away from home," he said.

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