The British death toll in Afghanistan this year reached 100 on Monday as another soldier was killed in the violence-scarred country, but London insisted the increasingly unpopular fight is not in vain.

The soldier, from 1st Battalion The Royal Anglian Regiment, was killed by small arms fire in Nad-e Ali in the troubled southern Helmand Province, the Ministry of Defence said in a statement.

His death brings to 237 the total number of British troops who have died in Afghanistan since operations began in October 2001. At least 205 were killed as a result of hostile action.

Prime Minister Gordon Brown said in a statement that every loss was a "real and personal tragedy", adding that British troops had to complete their mission.

"We will never forget those who have died fighting for our country and we must also honour their memory. That means staying the course, doing what is right for Britain, and seeing this mission through," he said.

Polls show the war has become increasingly unpopular this year, with Brown coming under severe criticism for his handling of the campaign and the government facing accusations that troops lack sufficient equipment.

The government has stepped up its efforts to explain why British troops are still there eight years after the campaign began, and spell out the road map towards troop levels being reduced.

Meanwhile London has struggled to convince its NATO allies to ramp up their troop levels to match its commitment.

Brown insisted British troops were having a "very real impact" on the ground.

"Our military presence in Afghanistan means that Al-Qaeda cannot use the country as a base from which to plot terrorist attacks against Britain," he said.

"And the work of our armed forces in the next stage of the campaign, the training and partnering of the Afghan security forces to do this job for themselves, along with the political and civilian development of the country, will be vital in ensuring the British people are safer for generations to come."

British regular troop numbers are rising by 500 to 9,500 this month. They are based in Helmand, where they are battling Taliban insurgents and training local forces.

A deliberate switch in tactics by the Taliban extremists towards using improvised explosive devices has made 2009 the bloodiest year for British forces since 1982 and the Falklands War with Argentina.

About three-quarters of the 100 deaths are thought to have been caused by IEDs.

The professional head of Britain's armed forces said his troops had brought greater security to Helmand and were helping local forces develop their capabilities.

"There is still much to do, and there will be difficult days ahead, but our armed forces are making a real difference, and are building the basis for enduring success in Afghanistan," Air Chief Marshal Sir Jock Stirrup said.

Meanwhile British Army chief General David Richards said: "The temptation to judge this essential campaign by casualties alone undervalues the tremendous efforts of our forces and our allies, and the progress they are making.

"There are real grounds for optimism. We have made substantial progress in Helmand and throughout Afghanistan.

"Political resolve is firm; the necessary resources and manpower will be flowing into Afghanistan to allow us to do the job."

The first British soldier to die in Afghanistan this year was Serjeant Chris Reed, 25, from 6th Battalion The Rifles, who was killed by an IED while conducting a vehicle patrol.

He was killed on New Year's Day.