Leading article: Missing in action: the failure of Mr Kennedy

It cannot have been much fun for Charles Kennedy, when he rose at Prime Minister's Questions yesterday, to be greeted with goodbye waves from the government benches. And the question the Liberal Democrat leader asked deserved better than the reception it received. To his call for an inquiry into the US practice of "rendition", the Prime Minister responded that there would be no inquiry and that the very idea that all US government flights to Britain should be investigated was "absurd".

While these non-answers may return to haunt Mr Blair - at least we hope they will - the exchange highlighted Mr Kennedy's predicament. The whispering campaign against his leadership has now spilled far beyond the inner circles of his party. Mr Kennedy was under huge pressure yesterday to make his mark. And to an extent he succeeded. When he does speak up, he usually has a contribution to make. His stance on Iraq, on the Government's repressive anti-terrorism measures and on civil liberties generally has been principled and consistent; it has given the Liberal Democrats a voice that set them apart from the other parties.

The disappointment, and it is a big disappointment, is that Mr Kennedy's voice has been heard so seldom. In May, the Liberal Democrats achieved their best general election result for 82 years. They attracted an additional 1 million votes compared with four years before, and they returned 62 MPs to Parliament. It might not have been the grand breakthrough the party had hoped for, but it was a creditable performance, and one Mr Kennedy lamentably failed to capitalise on.

The increased Liberal Democrat presence in Parliament was not the only asset that could have made this autumn Mr Kennedy's season. Labour's difficulties in coming to terms with its depleted majority opened up a real possibility for an assertive leader to force a transition to something akin to three-party politics. The weakness of the Tories as they went through the ponderous procedures of a leadership election was an added bonus. A more politically adept third-party leader would have rushed to fill the vacuum. All too often, Mr Kennedy was missing from the action.

Now, the Conservatives have a young and energetic leader who is pitching not just for a share of the Blairite centre ground, but for some of the territory - the environment, for example - that the Liberal Democrats have treated as their own. Yesterday David Cameron's immediate condemnation of the Government's decision not to hold a public inquiry into the London bombings left the Liberal Democrats looking tardy. If - as it appeared last night - Mr Kennedy is intent on remaining leader, he will have to sharpen up his act.

Of course, leading a third party in a system that is still relentlessly gladiatorial is not easy. But Mr Kennedy's failure to exploit so many opportunities since May has shown how far his leadership falls short. Whether he should step down now - when leadership change is in the air - or wait, to avoid the appearance of giving Mr Cameron his first scalp, is a decision he and those who are undoubtedly eyeing his job must weigh. What is beyond doubt is that the question is no longer if, but when.

And not just when, but who. The deputy leader, Sir Menzies Campbell, has kept the party on the political map over the war in Iraq and the whole area of terrorism with clarity and distinction. David Laws, the work and pensions spokesman, has done himself and his party much good in the pensions debate, as have Vincent Cable on the economy and Nick Clegg on Europe. With Simon Hughes a lacklustre party president, the party must prepare - as the Tories did - to test youth against experience. But it reflects well on the Liberal Democrats, as a small party, that they are blessed with such a choice.