There is no need for such lack of candour over Sierra Leone

General Sir Charles Guthrie is not in Sierra Leone today to oversee British disengagement from a former colony. The presence in Freetown of the Chief of the Defence Staff confirms that what has happened over the past week is not "mission creep", but a change in policy.

An ordinary member of the public, or of Parliament, might have accepted at face value the announcement eight days ago that British forces were being deployed to Freetown, the capital of Sierra Leone, to help to evacuate British nationals and others. Such a person might then have noted that this operation required making the airport secure. It then became clear that the airport could now be used to receive reinforcements for the 8,000 United Nations peace-keepers in the country, who are being overwhelmed by rebel forces bent on restarting Sierra Leone's civil war. Then that British officers on the ground saw their mission as being to roll up their sleeves, to help to support the legitimate, democratic government of Ahmed Tejan Kabbah, and to help to push back the rebels. Then that British troops were providing advice, surveillance and transport to Sierra Leonean government forces.

It is not a case of Britain being sucked inexorably into the conflict without meaning to be, as Lawrence Freedman pointed out in these pages on Saturday, but of the Government's policy shifting, without any change being announced.

There is absolutely no need for such lack of candour, one of the abiding failings of New Labour. The Government is doing the right thing and should be open and honest about its objectives, as well as about the limitations of British engagement and the risks to British forces. In Sierra Leone, of all places, Tony Blair and Robin Cook should realise that doing the right thing by stealth is asking for trouble. It is, after all, the exotic location of a previous botched initiative that was well intentioned but that embarrassed the Government over the hiring of mercenaries and the bending of UN sanctions rules.

They should say, therefore, that Britain has an obligation to do what it can, but that it cannot do everything. We cannot fight the civil war on behalf of the democratic forces in Sierra Leone. That would require troops in larger numbers than our overstretched armed forces could supply and more troops than the 11,000 the UN currently intends to deploy. No one knows how many troops it would require, or whether the UN policy of attempting to keep the peace rather than fighting the civil war can be made to work. What is clear is that the deployment of 800 British paratroopers to Freetown has had a stabilising effect, and British forces are likely to be part of UN-brokered attempts to resolve the crisis, even if they do not wear blue helmets.

In which case, Parliament should have been asked to vote, rather than being informed, disingenuously, that troops were being sent to help a few old ladies on to an aeroplane. It ought to be, but is not, as Tony Benn often points out, a constitutional principle that, whenever the lives of British service people are being put at risk, the House of Commons should approve their mission by formal vote. Mr Blair did once ask the House to approve action by the Royal Air Force against Iraq, but he seems to have regretted the precedent, because he sought to avoid a vote on the action against Serbia last year.

He would have won the vote then and strengthened his moral case. He would win a vote now, if he were to state explicitly what he is trying to do. That would be an ethical foreign policy.