A team of around 10 British troops has been deployed to Afghanistan to help local forces after the Taliban took control of key strategic sites in Sangin.
Soldiers have been mobilised to Camp Shorabak in Helmand as part of a wider Nato mission following days of fighting.
Ministry of Defence (MoD) officials insisted that British personnel are working in an advisory role only, but former military top brass have called on ministers to be prepared to expand British intervention.
Families of troops killed and injured in Afghanistan warned that the Government is "still not learning the lessons" from its past operations.
Sangin was the scene of fierce fighting during the full Afghan campaign, with more than 100 British troops dying in and around the town.
From the start of operations in October 2001, 456 British forces personnel or MoD civilians were killed in Afghanistan.
Lord Dannatt, former chief of the general staff, said the Government must think "long and hard" about any expansion of the UK's role as it balances other military demands while operating with a smaller Army.
"We can't do all of those things - the Government has got to decide what its priority is," the former head of the British Army told the BBC Radio 4 Today programme. "Something, however, must be done."
But Afghanistan is currently a "lower priority" than Libya and Syria, the peer said.
The Times reported that the latest deployment included at least one SAS unit of around 30 soldiers who were backing US special forces and the Afghan National Army, but the MoD refused to comment on the claims.
General Lord Richards of Herstmonceux, a former Nato commander in Afghanistan, told the newspaper that Britain and its allies should be prepared to increase the number of support troops in the country if needed.
He said: "It is important that the West honours its commitment to protect the Afghan people as well as the memory of those who fought and died there to keep us safe from extremism."
Defence select committee chairman Julian Lewis said British forces must be able to respond more flexibly to extremists in Afghanistan as well as in Iraq and Syria.
He told BBC Radio 4's World At One: "What we ought to be doing in all these countries is having a flexible force which can swoop in and swoop out again, a mixture of special forces supported by air power in support of friendly ground forces where they exist.
"But we should resist getting drawn in permanently to build up a nation in a country that is not ready for it."
Diane Dernie, whose son Ben Parkinson lost his legs and was left brain-damaged by a bomb in Afghanistan in 2006, said she feared the Government was "still not learning the lessons and that it's British troops that are going to pay the price for that failure to learn".
Judy Gaden, whose son Corporal Tom Gaden was killed by a bomb in 2009, said it was "tragic" that a "fuller picture" was not looked at before troops are deployed.
An MoD spokeswoman said: "As part of the UK's ongoing contribution to Nato's Resolute Support Mission, a small number of UK personnel have deployed to Camp Shorabak in Helmand province in an advisory role.
"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.
"In total the UK has around 450 troops in Afghanistan mentoring and supporting the Afghan National Defence and Security Forces and the Afghan Security Ministries."