Defence Secretary Dr Liam Fox has announced the deployment of the UK's Theatre Reserve Battalion and the redeployment of British troops from Sangin to central Helmand, as part of changes being made to the international force structure in southern Afghanistan.

The changes will better reflect circumstances on the ground and the earlier division of Regional Command (South) into two separate commands.

Dr Fox told Parliament that the elements of the UK Theatre Reserve Battalion, currently provided by 2nd Battalion The Duke of Lancaster's Regiment (2 LANCS), will deploy temporarily at the request of the International Security Assistance Force (ISAF) to central Helmand province in mid-July. These additional forces, some 300 in total, will give commanders the additional flexibility over the summer to reinforce progress in central Helmand.

This deployment will precede the phased reorganisation of international forces across the newly-created Regional Command (South West), reflecting the deployment of more than 18,000 additional ISAF troops to the province over the past 18 months.

The British presence in Sangin will be moved when the current tour of 40 Commando comes to an end. It will be replaced by US forces.

The Chief of the Defence Staff, Air Chief Marshal Sir Jock Stirrup, said: "The temporary deployment of the Theatre Reserve Battalion will allow ISAF to build on the significant progress we have already made in central Helmand and to drive home improvements in security, governance and infrastructure. These forces are also an essential precursor for the next stage of the reorganisation of ISAF forces in Helmand in which we will hand responsibility for Sangin to our American counterparts."

"This reorganisation makes very sound military sense and ensures that UK troops are deployed in the most effective way alongside ISAF and Afghan forces."

"Our Service personnel can rightly be enormously proud of the work they have done in Sangin and the significant progress that they have achieved there. Sangin is a challenging area of Afghanistan and we leave it a better place. The experience our troops have gained there will be vital in the work they will continue in the important population centres of central Helmand."

The changes in Sangin are able to be made because ISAF intends to restructure its forces in Farah and Nimruz provinces and in northern Helmand, so that it can consolidate a US Marine brigade in the Upper Helmand Valley which will assume responsibility for security in Sangin later this year.

This in turn will enable UK troops to be redeployed to reinforce progress in the key districts of central Helmand, allowing those deployed as part of our Theatre Reserve Battalion to withdraw.

ISAF's plan will tidy up the current arrangement where British forces in Sangin come under US command. The result will be a coherent and equitable division of three brigade-sized contributions, with the US in the north and south, and the UK-led Task Force Helmand, with our Danish and Estonian allies, in the central population belt.