Gordon Brown paid a surprise pre-Christmas visit to British troops in Afghanistan's Helmand province today as the operation to retake the opium-trading bazaar town of Musa Qala reached its climax.

The Prime Minister arrived shortly after 7am at Camp Bastion, the main British base in Helmland around 60 miles from Musa Qala - the frontline where approximately 3,000 British troops were today close to capturing the only sizeable town controlled by Taleban insurgents, and where Afghan troops made a reported breakthrough this morning.

Mr Brown arrived by RAF Hercules on the second leg of his pre-Christmas tour, after visiting British troops in the southern Iraqi town of Basra on Sunday. It was believed to be the closest a serving Prime Minister has come to a warzone since Tony Blair visited Kosovo during the conflict there in 1999.

Mr Brown paid tribute to the troops' courage and bravery, and thanked them for their public service over Christmas.

Flanked by Des Browne, his Defence Secretary, Mr Brown addressed a gathering of some 300 troops. He said: "This is one of the most challenging of environments, one of the most difficult of tasks, the most testing of times, and one of the most important of missions, because to win here, and defeat the Taleban, and make sure we can give strength to the new democracy in Afghanistan, is important for defeating terrorism around the world.

"I know that we can win in Musa Qala. Some of you here - and many of you not here but up there - have been doing a very important job in clearing the Taleban.

"I know the work you are doing today and over the next few days is important to the whole mission in Afghanistan. I believe, if we can succeed there, which we will, and we can work with the Afghan forces, then we can move forward to a more peaceful future for this country."

Around 2,500 troops are based in Camp Bastion, with hundreds flying the 30 minute journey to the frontline in Musa Qala. The base also hosts the regional hospital, and has received casualties from the battle over the last few days, although officials would not say how many.

A spokesman for the Nato-led force said that Afghan army troops entered the centre of Musa Qala today, on the fourth day of the operation to recapture it. but fighting was continuing. In Kabul, a Defence Ministry spokesman said that Afghan, British and US forces had "completely captured" the town.

A British military spokesman, Lieutenant Colonel Richard Eaton, said that he could not confirm that the Taleban had left the town’s centre but said he would not be surprised if that were the case.

"This is what happens. We have had a number of operations in the past where once the Taleban realize they are overmatched, they tend to leave," he said. "I wouldn’t be surprised if that is the case here. Ultimately our aim is to take Musa Qala, and if we take Musa Qala without a big fight, that’s fantastic."

The operation is one of the biggest against the Taleban since the invasion in 2001. It was launched after weeks of air strikes and probing attacks had softened up their defences and killed hundreds of their fighters.

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