Kim Sengupta: This is a done deal, but the Lib Dems are unlikely to support it

There will be criticism of the passing of command after all the sacrifices that have been made

Liam Fox made a good first impression at the Ministry of Defence. The department has been subjected to upheaval and uncertainty thanks to a revolving door of ministers. Dr Fox said he intended to stay for five years as Secretary of State. He also earned kudos from the staff by avoiding cheap jibes about his Labour predecessors.

Now comes the hard part. Dr Fox will have to deal with a Strategic Defence Review with the three service chiefs fiercely competing for their share of a reduced cake. The fudge with the Liberal Democrats in the pre-nuptial agreement for the coalition government over Trident will have to be addressed. But, as Dr Fox said on taking office, the priority is Afghanistan.

The new Defence Secretary takes over at a time when the role of British troops in Helmand is going through fundamental changes, the main one being that they will be reporting from 1 June to Major General Richard Mills of the US Marine Corps, instead of Major General Nick Carter of the British Army.

There will, undoubtedly, be criticism of the passing of command after all the sacrifices that have been made in Helmand. But the reality on the ground is that the Americans will be taking the lead in large-scale missions in the future, as they did recently in Marjah. Under the circumstances, it is unsurprising that they should want to be in overall charge.

British troops will focus on protecting populated areas where reconstruction is taking place. This was the strategy of General Sir David Richards, the British officer then commanding Nato forces in Afghanistan, which was undermined when UK forces were sent to fight the Taliban in outlying areas such as Sangin and Musa Qala, triggering the insurgency still flaming across the province.

The transfer of command is a done deal, although it has yet to be officially confirmed. The next part of the plan of General Stanley McChrystal, the head of Nato's Afghan force, is not. He wants British forces to move from Helmand to Kandahar to replace the outgoing Canadians. Washington has even offered to underwrite a sizeable part of the substantial costs. The previous government and the head of the military, Air Chief Marshal Sir Jock Stirrup, were all adamantly opposed to the Kandahar move. Gen Richards, now head of the Army, and a number of senior officers would like a feasibility study to be carried out before any decision is made.

The Kandahar option would be a bold move for the new government and may assuage some of the rancour with the Americans over the hasty withdrawal, against their wishes, from Basra. The chances of Dr Fox's Liberal Democrat partners agreeing to this, with many of the party membership intrinsically opposed to the war itself, appear to be pretty slim.