According to the respected World Conservation Union, via its annual “Red List”, the planet contains some 16,306 species that are “vulnerable, endangered or critically endangered”. These include 51 per cent of invertebrates, 39 per cent of fish, 31 per cent of reptiles and amphibians, 20 per cent of mammals and 12 per cent of birds. What could become obvious in Brighton in the coming days is that the number of these poor creatures is actually rather higher. The addition involves everyone in charge of the Liberal Democrat Party.

The issue of the party’s leadership has even made it, in a subliminal fashion, into the conference agenda. This accidentally taps into a mood that combines both activists and MPs lurking in dark corners waiting to wield the dagger and those determined to defend Sir Menzies Campbell. How else could one explain a schedule that allows his question-and-answer session this afternoon to be followed by a discussion about bullying, and which precedes his final address with an examination of “the surveillance society”? The most appropriate session of the week, however, occurs early on Wednesday morning. It is entitled “Taking Action to Tackle Excess Packaging”. Sir Menzies can be accused of many things, but excess packaging has certainly not been a feature of his leadership.

In present political circumstances – uninspiring poll ratings and a disappointing set of election results in May – it is not surprising that some Liberal Democrats believe that a change at the top is essential. Indeed, in a survey by Populus for The Times today, two thirds of Liberal Democrat voters believe that if the party is to make an impact then it must “replace Ming Campbell with a younger and more charismatic leader”. That this would be the first time in history that any political organisation has replaced one leader for being too drunk followed by another for being too sober seems to be immaterial. Daniel Finkelstein, writing on these pages a fortnight ago, carefully weighed the evidence before declaring that the Liberal Democrats have a leader who is “useless” and should therefore be “dumped” immediately.

Yet if there are any Lib Dems who believe that their party would experience an equivalent of a “Brown bounce” if they heeded this advice, they are destined to be disappointed. There is, indeed, a “leadership issue” – but it is not so much to do with their own chieftain as those of the other two parties.

The truth is that the difficulty for the Liberal Democrats is essentially strategic. There is no longer the political space available for them to hold the same share of the vote that they achieved at the past general election and they are simultaneously suffering from both an invisibility and an identity crisis. Their most profound need now is not a new leader but some new and memorable slogans.

It is the lot of a third party in the British system that it is always vulnerable, periodically endangered and occasionally (as the Liberal Party was in the 1950s) critically endangered. If Labour or the Conservatives find a fresh leader, shift their position on the ideological spectrum, or trumpet new policies, they can affect their standing with the electorate (if not always to their advantage). The same is hardly true for the Liberal Democrats. They are dependent on the actions of the other two parties.

It is this – and not anything directly related to Charles Kennedy – that explains why the Liberal Democrat share of votes cast rose between 2001 and 2005. The controversy surrounding Tony Blair’s support of the war in Iraq (plus a weariness with his tenure), together with Michael Howard’s “core vote” appeal to right-wing Conservatives, created the opportunity for the Liberal Democrats to prosper. All that Mr Kennedy had to do was decide to oppose the removal of Saddam by the United States and Britain. It was the single decision of his in that Parliament that had lasting significance.

Sir Menzies now confronts entirely different territory. David Cameron was prepared (at least at first) to shift the Conservative Party to the centre, draining support from the soft-right flank of the Liberal Democrats. Labour has replaced a Prime Minister whose popularity had waned and altered policy in a number of areas. This has inevitably chipped away at the soft-left wing of the Liberal Democrats. The party’s showing in the polls would have slipped to about its present point if Mr Kennedy had remained leader, or if Chris Huhne or Simon Hughes, not Sir Menzies, had been his successor. The key to any revival rests in either (preferably both) of the major parties making big policy mistakes or lurching to left or right.

Without that happening, the Liberal Democrats will not escape their 16-17 per cent rating in opinion surveys this year – support very similar to that they had in 1992, 1997 and 2001.

What small improvement (one or two percentage points of the national vote) they can achieve beyond that depends on developing a tiny number of policies, basically slogans, that are uniquely linked to them. There is a dearth of such policies at the moment. Old calls for more spending on this or that have been overtaken by Labour’s expenditure. It will not be long before the Iraq issue disappears. None of the policy commissions that have reported lately has passed the test of devising a compelling sentence reading “You should vote Liberal Democrat because . . . (then add at most seven more words)”.

That is what the party should be concentrating on at its conference. It might, nonetheless, not happen. And even though the World Conservation Union has issued a warning that vultures are in danger of becoming extinct, Sir Menzies might well spot some circling at Brighton.

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