About 80 British soldiers travelled to Sangin to fight Taliban insurgents with the Afghan National Army (ANA), just months before it takes full control of security in the country.
The latest mission, which was kept secret until after it was completed earlier this week, required the special permission of Defence Secretary Philip Hammond because of a Government push to transfer combat operations to the ANA, The Sunday Times reported.
In recent months the British Armed Forces have instead been focusing on mentoring the Afghan National Army in preparation for their withdrawal from the country next year.
The MoD said specialist advisers from the Brigade Advisory Group, made up of the 4th Battalion The Rifles, provided support to the UK-mentored 3/215 Brigade for the eight-day mission.
“In support of the Afghan forces who now have the security lead across the country, UK personnel do on occasion operate outside the usual UK area of operations in central Helmand in an advisory capacity, “ the Ministry of Defence said in a statement.
“These out-of-area operations have been a long-standing element of the UK mission in Afghanistan and are completely in line with our current role of providing training, advice and assistance to the Afghan National Security Forces.”
The statement added that Sangin “remains a challenging area”. There were no British causalities but a number of ANA soldiers were killed.
Brigadier Rupert Jones, Commander Task Force Helmand, said: “It has been a very impressive demonstration of what the Afghan National Army can be capable of.”