President Bush has announced the beginning of US withdrawal from Iraq, and the MoD is assuming that just a few hundred British soldiers will remain in Basra after spring 2009. But Gordon Brown is unlikely to declare “mission accomplished”. Not only would that invite unhappy comparison with President Bush on the flight-deck of the USS Abraham Lincoln, it would imply a coherence to the Iraq mission that not even Tony Blair dare claim. A more botched campaign is hard to imagine. Yet it could happen again.

One reason is that we don't really know why it went wrong. Another is that ministers believe it all stems from Mr Blair's decision to throw in unconditionally with the White House. But between a grand-strategic decision and ground operations is a world of planning. Strategic ends are won by smart campaign planning, campaigns are won by well-judged battles and battles by sound tactics. There are no shortcuts. Why were our tactics - military and civil - so inadequate and so out of synch with the Americans at the outset of the insurgency? And why, when the US changed approach with the Petraeus troop “surge”, were we so hamstrung? During Operation Charge of the Knights, the US-Iraqi offensive against Basra militias last May, we were mere spectators. In Parliament, Des Browne, the Defence Secretary, dismissed that embarrassment, saying: “Iraqi security forces, supported by UK Forces and coalition partners... have been successful.” As Professor Joad of the Brains Trust would have said, it depends on what you mean by “supported”.

We won't know why Iraq went so wrong until we dig deeper. An inquiry is long overdue. For two years the Government has promised one “at the appropriate moment”. But as Sir Menzies Campbell said in the Commons a year ago, the right time is while the relevant ministers are still in office and applicable MPs still in Parliament (he might have added “and while senior officers are still serving”): Gordon Brown must now initiate that inquiry.

One thing can't wait any longer: better formulation and co-ordination of strategy in the War on Terror. In Washington we have a two-star officer as defence attaché and head of the network of liaison officers at various research and training establishments, currently a shrewd major-general, Peter Gilchrist. We have a one-star general in the Pentagon, and a two-star at Centcom, the planning headquarters for Middle and Near East campaigns. This, supposedly, gives us input to campaign planning, but as our military contribution is so small, we can't expect much. When, for example, it looked as if Britain might not take part in the actual invasion in 2003, Donald Rumsfeld, then the US Defence Secretary, brushed it off as a minor inconvenience. In war - unlike diplomacy - you can't punch above your weight.

Nor is our operational expertise seemingly much valued. There has always been Anglo-US military rivalry, but it was founded on mutual, if grudging, respect. There is evidence now of a loss of respect among US officers for our capability and commitment. This will need working at (refocusing on Afghanistan is both a challenge and an opportunity), but we must accept that our influence at campaign level is weak.

The level at which we have really failed however, is “military-strategic”, where guidance is formulated for campaign planners. Strategy is not decided behind closed doors in the Oval Office. The Chairman of the Joint Chiefs of Staff is the President's principal military adviser as well as the Defence Secretary's, although responsibility for the execution of campaigns falls on combatant commanders. We have no heavyweight liaison at this level, yet it is here that we might have the greatest leverage because strategy is the application of the entire resources of the nation, not least the intellectual (and we do still have - as the Americans call it - impressive “operational heritage”). Few in America would argue that the “war against terror” can be conducted without allies; few could think there is any more capable ally than Britain.

There is a model for co-operation at this level. In Arlington National Cemetery is a statue (equestrian, as befits a field marshal) of Sir John Dill, the former Chief of the Imperial General Staff who, from 1941 until his death in November 1944 was the permanent British representative to the Combined (Anglo-US) Chiefs of Staff Committee that steered Roosevelt and Churchill's military strategy. Roosevelt called Dill “the most important figure in the remarkable accord which has been developed in the combined operations of our two countries”.

With both John McCain and Barack Obama indicating a willingness for greater co-operation, the sooner we reconstitute that committee, with a representative of Dill's stature, the sooner we regain some control of defence planning.

Churchill understood strategic co-operation, even if he was sometimes uncomfortable with the consequences. As well as ordering an inquiry into Iraq, Mr Brown should show some Churchillian resolve, and grasp the strategic nettle.

Allan Mallinson is a military historian, novelist and former cavalry officer

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