It would be easy to treat the current travails of the Liberal Democrats with a mixture of bemusement and schadenfreude. A party which purports to reject confrontation and claims to prefer a continental-style form of consensus politics over the ‘yah-boo’ adversarialism of Westminster has now stabbed its leader in the back twice in the space of 18 months. As they say of student politics, the lower the stakes, the more vicious the fight.

As has been widely noted, for Menzies Campbell to have carried the can for his party’s current poor poll ratings is somewhat unfair. Younger Liberal Democrats might have been better advised to ponder what those with longer memories well-know: that, unlike the two main parties, the third party’s ability to control its own fate is somewhat limited. The strength of the Liberal-SDP Alliance in the 1980s rested on Labour’s weakness, while the Liberal Democrats’ resurgence during Tony Blair’s premiership stemmed from the unelectability of the Tory party.

Unsurprisingly, during the late Thatcher and early Major years, when the competition between Labour and the Tories became more even, Lib Dem support fell sharply. Indeed, let’s not forget that the Lib Dems’ supposed breakthrough in the 1997 election was simply the outcome of the vagaries of the British electoral system which the party so deplores. Its share of the vote in that election was actually its lowest in nearly two decades.

And there is nothing recent about this phenomenon: throughout the postwar period, the Liberal party’s support has risen and fallen – down in the 50s and 60s, up in the 70s and 80s – due to external factors which appear to have little to do with the performance of its leaders or the coherence of their policies.

The Liberal Democrats were thus always going to struggle in a period where the revival of the Conservative party under David Cameron was swiftly followed by the renewal of the Labour party under Gordon Brown. But that is not to say that the Lib Dems are simply passive victims of the situation they now find themselves in. Under Charles Kennedy – although, ironically, less so under Campbell – they traded intellectual and ideological consistency for short-term political advantage.

This reached its apogee in 2005 when, confronted by the rich pickings of Michael Howard fighting a core vote campaign and an Iraq-tarnished Tony Blair, Kennedy attempted to feast on entrails to his left and right. The Lib Dem strategy was exemplified by a 10-point programme which displayed the worst kind of interest group politics, devoid of an overarching vision and stripped of any attempt to confront the tough choices facing a party purporting to be serious about government. Kennedy’s gamble fell short of expectations and left him with a parliamentary party riven by very different priorities: while some of his MPs owed their seats to leftwing urban protest votes, others were the beneficiaries of liberal Tory voters in the shires unable to stomach the idea of Howard in No 10.

On Iraq – perhaps the Lib Dems’ defining issue over the last five years – the party’s attitude was especially cynical. While their opposition to the conflict was shared by many others in the country (and, indeed, the Labour party), their apparent insensitivity to the human rights abuses perpetrated by Saddam’s regime and their continuing refusal to accept Britain’s postwar moral responsibilities to the people of Iraq is a betrayal of the kind of liberal internationalist principles displayed by Paddy Ashdown in the face of mass murder in Bosnia and Kosovo.

That is not to say, however, that the Liberal Democrats’ influence on the policy debate over the past few years has been entirely malign. On a number of issues – their support for further constitutional reform and the localism agenda, advocacy of green taxes and, more recently, despair at Britain’s ever-growing prison population – the Lib Dems have earned the right to have their arguments taken seriously. Indeed, Nick Clegg’s recent advocacy of an earned amnesty for illegal immigrants was a brave and useful intervention into a debate which for too long has been mired by political calculation. Labour should therefore beware that, under a new and more determined leader, the Lib Dems are not allowed to stake out new progressive ground which it should rightfully occupy.

So where do Labour’s interests lie in the debate about the Lib Dems’ future which will no doubt be aired in the upcoming leadership election? A third party committed to localism and public sector reform would strengthen the hands of those in Labour’s ranks committed to such an agenda. And it would enhance the Lib Dems’ chances in those middle England seats where it needs to fend off a Tory revival. Labour’s interest in these seats remaining in Liberal rather than Conservative hands is obvious.

Thus in the battle between the Lib Dem modernisers and the reactionaries, Labour’s sympathy should be firmly with the former.