British forces in southern Afghanistan will be led by 4th Mechanized Brigade from April 2010, Defence Secretary Bob Ainsworth has announced.
The routine rotation will install 4th Mechanized Brigade as the UK's lead formation in Helmand province.
They will replace 11 Light Brigade and be in command of the majority of units serving in the country.
There are currently more than 10,000 UK troops deployed in Afghanistan, including about 500 special forces.
Mr Ainsworth announced the deployments in a written statement to the House of Commons.
The deployment - which does not change overall force levels in Afghanistan - will include 40 Commando Royal Marines, the Royal Dragoon Guards, the Queen's Royal Lancers, 1st Battalion the Scots Guards and the Royal Scots Borderers.
It will also include 1st Battalion the Duke of Lancaster's Regiment, 1st Battalion the Mercian Regiment and 1st Battalion the Royal Gurkha Rifles.
Prime Minister Gordon Brown said although deployments had been announced, the objective of bringing UK forces home remained.
Speaking on a visit to a housing estate in Stevenage, Hertfordshire, he said: "Our aim is that the Afghan army itself is strong enough, and the police is stronger, so that they can take over control of the country and we can gradually bring our troops home."
The 11 Light Brigade, which was formed specifically for Helmand, replaced 19 Light Brigade in October 2009.
The latter lost 70 men during six months of fighting.