Gordon Brown’s diffuse mission to Washington would have seemed more coherent if he had given a clear statement on what Britain intends to do in Iraq before he got on the plane.

He did, mind you, on his departure, deliver a resounding declaration that Britain would now step up pressure against Zimbabwe, finally abandoning the unsuccessful tactic of silently “working behind the scenes”.

But Britain’s goals in Iraq are still a cipher, to the US, to Iraqis and to the region. Plan A, of slithering out with staged cuts in troop levels, is probably now unachievable given the problems boiling up in southern Iraq. But if so, Britain needs to say clearly that it is there to stay, and work out what its 4,000 troops are supposed to be doing, or it will have the worst of all worlds.

This was illustrated this month, when violence flared in Basra, and the Iraqi Prime Minister, Nouri al-Maliki, called on American forces in Baghdad to help, without even telling the Brits. That leaves British Forces redundant, humiliated and, in being openly scorned by the Iraqi Government, even more vulnerable and exposed.

At the same time, the new violence in the south means that pulling troop levels down in the near future, the plan that Brown announced in the autumn before the election he didn’t call, is difficult to uphold. It would strain relations with the US, the opposite of what Brown says he wants from this week’s effort in Washington. It would also sacrifice Britain’s remaining influence in the Iraq conflict, and its ability to retrieve anything from the mess. There is exasperation and worry in Arab capitals that Brown’s Government has given them little attention. They feel neglected in favour of Asia.

It is not a bad time at which to clarify Britain’s commitment. Astonishingly, there have been three positive steps forward in two weeks — improvements in Iraq’s previously paralysed political situation — even though violence has suddenly spiked again. That reverses the pattern of the past year, of military success and political failure. The changes are good news because, without political progress, Iraq will get nowhere.

One important step is that yesterday Sunni politicians agreed to rejoin al-Maliki’s Shia-majority Government, which they left last year. Without a joint government, hopes of Iraq knitting together are zero, whatever the current reading on the barometer of violence.

The second is that al-Maliki this month sent in Iraqi forces against Shia militias who had been battling for control of the country. Yes, many of the newly trained soldiers ran away, but many didn’t, and the assault appears to have given the militias a significant shock.

Thirdly, Nato yesterday agreed to become involved, albeit through training forces and sending equipment, not combat. This new era of relations between the 26-member alliance and Iraq is an important step in stabilising the country. Nato was split over the 2003 invasion, and its help has been limited to small training missions.

These changes point to a way forward where there has been none, based on Iraqi politicians’ new willingness to act as a government. But Britain does now need to tell the US, Iraqis, and its own forces what part it intends to play. As Michael Clarke, head of the Royal United Services Institute, points out in a recent thoughtful paper, British units in Iraq and Afghanistan have sustained casualties of up to 11 per cent, “a Second World War casualty rate”. That is cripplingly demoralising if the soldiers and the rest of Britain are not sure why they are there.

First (under Tony Blair), Britain was staying in Iraq until the end. Then, it was going to leave slowly. Then (under Brown), more quickly. Now it is staying (probably). As with Zimbabwe, Brown’s instinct may be to preserve his options by saying little in public. But as a tactic in this case, silence will not do much to help Iraq, or Britain.

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