By Paul Reynolds
BBC world affairs correspondent
The planned deployment of another 3,500 British troops to Afghanistan is part of a big new push by Nato forces to pacify the south of the country.
UK troops will be stationed in the south of Afghanistan
It would bring the British and other forces much more into the Afghan combat zone than before.
There are twin problems in the south. First an insurgency led by the Taleban is developing there - with suicide bombings as a new tactic, apparently copied from Iraq.
And the growth of poppy cultivation for conversion into heroin is hindering efforts to develop a normal economy.
The move is timed to coincide with an international conference on support for Afghanistan in London on 31 January and 1 February.
The conference is expected to agree an "Afghan compact" to take forward aid to Afghanistan, which has already amounted to about $16bn.
This would set benchmarks for progress in a number of areas such as security and good government and a system to monitor progress.
The plan is that the British troops, which will be a strong military force led by paratroopers and with Apache helicopters, will join three other contingents from Canada, the Netherlands and the US.
They will replace an existing and smaller US force and the deployment is an extension of other such forces elsewhere in the country.
The final stage into the south east is due to be carried out later this year.
The troops form what are known as Provincial Reconstruction Teams. That means their role will not be wholly military.
Like this Italian soldier, UK troops will be involved in handing out aid
They will also help to undermine the drugs trade by chasing drug traders and encouraging regular agriculture but inevitably the fear is that they will also get drawn into fighting.
The British will be in Helmand, the Canadians are already in Kandahar, the US will continue in Zabul and it is planned that the Dutch will go to Oruzgan.
However, there has been some resistance in the Netherlands to this deployment and although the Dutch cabinet has approved it, the Dutch parliament will have to vote on it in early February.
"We would welcome a Dutch deployment but if this is not possible, then it is for Nato to discuss," said an official of the Foreign Office in London.
The troops will be part of the Nato-led International Security Assistance Force (Isaf) and their stated role is defined by the planners as more "anti-insurgency than anti-terrorist".
The latter is carried out mainly by coalition forces led by the US.
However, a British official said that there would be more "synergy" between the two forces in the future and it is unclear how the division will be maintained if the insurgency grows.
One key aspect of the taskforce will be to cut down on the drugs trade.
"The drug operators pretty well roam freely," the British official said.
Farmers will be encouraged to grow alternate crops for poppies
The idea is not just to eradicate the poppy fields themselves (that work is done by locally hired Afghans, employed by local governors or US contractors) but to encourage other crops and build up rural economies and law enforcement.
The UN reported a 21% fall in poppy cultivation in 2005 but the problem remains a huge one.
The London conference will launch a Counter Narcotic Trust Fund to which Afghan allies will be asked to contribute.
Stable, but fragile
The insurgency in the south is a disappointment to international supporters of Afghanistan.
At the same time, the assessment is that the country is, in the phrase of the British government, "stable but fragile in areas".
There has been a good deal of progress - parliamentary elections were held last year, the economy has grown rapidly and millions of refugees have returned.
But the fact that a major troop reinforcement is being planned shows that there is some way to go.