Leading article: We've made enough mistakes already. Caution is now key

That there should be cross-party agreement on foreign policy at times of crisis is a convention observed more scrupulously in the United States than in Britain. Yet the ferocity of Ed Miliband's attacks on David Cameron at Prime Minister's Questions yesterday exposed the Government's growing vulnerability on Libya as the fighting there spreads. The unfolding drama in North Africa has not, to put it mildly, shown the Coalition at its best.

Nor, despite a sharp put-down about how he was not one to "knife a foreign secretary", was Mr Cameron able to silence the mutterings about William Hague's performance in the job. Mr Hague had suffered his own torment at the Despatch Box on Monday, taking a verbal bombardment on the apparently botched special forces mission to Benghazi. Yesterday, Mr Cameron assumed "full responsibility" for the operation, "as for everything that my Government does", but he had to be prompted to support Mr Hague, whom he eventually described as "an excellent foreign secretary".

None of this inspired great confidence either in the unity or – to use Mr Miliband's word – competence of the Government in the face of its first serious foreign policy challenge. Which might matter less if events in Libya showed any sign of an early resolution. Instead, the country seems to be hurtling towards all-out civil war, making the dilemmas for the outside world more complex almost by the hour.

Not that formulating a cogent response to developments in Libya, or across the region generally, was ever going to be simple. It is not just the last government's "special relationship" with Colonel Gaddafi and other undemocratic leaders that complicates things – though it does not help. It is that events – even in Tunisia and Egypt, where change came about relatively peacefully – are still in flux, and even the short-term outcome cannot be foreseen. The opposition in Libya is divided and Colonel Gaddafi's counter-attack calls into question whether even Benghazi can hold out. The most experienced government could be forgiven for procrastinating in such circumstances.

Still, the Foreign Secretary has seemed especially accident-prone. Left in charge of the shop while both the Prime Minister and his deputy were away, he appeared reluctant to recognise the scale of the emergency and was far slower than his foreign counterparts to authorise the evacuation of British citizens. He repeated an unconfirmed, and wrong, report that Colonel Gaddafi was on his way to Venezuela; then there was the now notorious SAS expedition. He also described Mr Cameron's early mention of plans for a no-fly zone as "overblown". Each of these mis-steps might have an explanation rooted in poor advice, misleading information or fast-moving events, but together they do not give the impression of sure-footedness.

The question now concerns the desirability – and feasibility – of a no-fly zone. That this is back on the agenda after Mr Cameron's early call for just such a measure suggests he may have been encouraged – by the US? – to float the idea. But Washington is right to insist that any such action be co-ordinated internationally and have UN authorisation. As the US Defence Secretary, Robert Gates, warned, even this seemingly minimal step would be tantamount to a declaration of war.

If Colonel Gaddafi's onslaughts on his own people intensify, it will be ever harder to stand idly by. But the internationally recognised "responsibility to protect" has to be set against the perils of intervening in someone else's civil war. It is not something to be undertaken lightly.