The Ministry of Defence says British personnel are there to advise the Afghan military and will not be taking on a combat role in the area.
British troops have been sent back to Helmand province in Afghanistan as reports indicate that the Taliban is close to taking a key strategic town in the region.
Local officials say that an onslaught from Taliban forces had left the Sangin and its surrounding hills “on the verge of collapse”.
The district in the opium-growing heartlands of Helmand province saw some of the heaviest British losses during the 13-year war. More than 100 British soldiers died in the area.
The Ministry of Defence (MoD) said UK military personnel will play an advisory role, helping Nato and Afghan forces to fight the insurgency.
The troops will not being going into combat and will not be leaving the military base where they are based.
Britain still has about 450 troops there to mentor and support the Afghan army and security forces, said a small number of personnel had been deployed to Helmand. They are returning to the province a little over a year after David Cameron hailed the end of the 13-year intervention.
The Times reported that the latest deployment included at least one SAS unit of around 30 soldiers who were backing American special forces and the Afghan National Army as they try to retake Sangin, in Helmand province, from the Taliban.
The MoD refused to comment on any operations involving the SAS.
Helmand also remains one of the deadliest areas for Afghan security forces, with some estimates saying around 2,000 soldiers have been killed or wounded in the year up to November.
On Sunday, Helmand’s deputy governor, Mohammed Jan Rasulyar, was pleading with the Afghan government to send in reinforcements. He said 90 members of the Afghan security forces in the previous two days.
“Your Excellency, Helmand is standing on the brink and there is a serious need for you to come”, he wrote in an unprecedented message on his Facebook page.
He said the Afghan police were holding out against Taliban fighters who had surrounded their compound and the district governor’s building in Sangin but roads into the town were completely controlled by the Taliban.
Mohammad Dawood, a police commander in Sangin, told the BBC by satellite phone that he was surrounded by casualties, and he and his men hadn’t eaten for two days.
“We only have the police HQ under our control and have a battalion of the national army with us. The district office and the intelligence directorate are under enemy control”, he said.
An Mod spokesman said: “These personnel are part of a larger NATO team, which is providing advice to the Afghan National Army. They are not deployed in a combat role and will not deploy outside the camp.”
Jawad Ludin, former deputy foreign minister of Afghanistan, told the BBC that Afghan forces are “losing 100 people every day” while Taliban losses are “even greater”.
However, he said he does not believe more combat forces are needed – what is needed is support.
Six American troops were killed in Afghanistan on Monday when a suicide bomber on a motorbike struck their patrol near Bagram air base.
British troops were first deployed to Sangin in 2006 in an effort to take on local opium drug lords, whose products, the British Government said, ultimately ended up sold on British streets as heroin.
The war on opium sellers was quickly abandoned after they made an alliance with the Taliban and focus of the troops shifted to defending their military bases.