The Liberal Democrats were on the brink of crisis last night after one of the party’s most senior MPs warned Sir Menzies Campbell that he “has to do better”.

Simon Hughes, the party president and former leadership contender, said that although Sir Menzies had “improved considerably” since taking the helm 18 months ago, he still needed to raise his game.

He also delivered what may be seen as a veiled threat, telling the GMTV Sunday Programme that the leadership was “always an issue”.

“[Sir Menzies} knows all the time that the party has to do better — that’s my job, collectively, and the leader obviously has to do better: get better at getting the message across better, at getting the policy out better, at making sure that out there people understand that Labour and Tory are often the same on policy. We offer a difference. Now, he will do that. I’m confident he’ll do that.”

Mr Hughes praised Sir Menzies’s speech, given at last month’s party conference in Brighton, and said that he seemed to be “up for the job”. But he added that the leadership was “always an issue in all of the parties”.

“We live in a presidential system, and therefore the leader has to continually do well and better.” Asked if he meant Sir Menzies had to do better, Mr Hughes replied: “Well, of course.”

A spokeswoman insisted that Mr Hughes was being supportive of Sir Menzies. “It’s very strong and very positive for Ming. The media is ignoring us and we must get our message across better, and Simon has shown he is very strongly behind Ming.” This is not the first time that Mr Hughes has spoken out, criticising Sir Menzies’s performance at Prime Minister’s Questions last year. Asked if Mr Hughes’s position was secure, the spokeswoman replied: “Absolutely”.

Research by Ipsos MORI for The Sun put the party’s support at just 11 per cent — compared with nearly 23 per cent at the last general election. Earlier in the week, a Populus poll for The Times put the Liberal Democrats down three points to a new low of 12 per cent.

More extensive polling by Populus before last month’s Liberal Democrat conference spelt trouble for the Lib Dem leader, with 67 per cent of party supporters saying that Sir Menzies should be replaced with a younger and more charismatic leader. This contrasts with members of the parliamentary party, who believe that it would be unwise to change leaders at this point.

Public jockeying between two of the party’s rising stars — the environment spokesman Chris Huhne and the home affairs spokesman Nick Clegg — dominated last month’s conference. Sir Menzies was widely seen to have bought himself time with a solid speech, and both have ruled out standing for the leadership against him.

However, with the possibility of Gordon Brown calling a snap election now removed, questions appear to be surfacing again over whether he is the right man to take the party forward.

Liberal Democrat MPs have been unhappy at their inability to communicate effectively, allowing the other parties to eclipse them almost entirely. In particular, there was some disquiet at the party’s failure to point out that both the inheritance tax policy and the aircraft tax, announced by Alistair Darling in the Pre-Budget Report, were Liberal Democrat ideas.

Sir Menzies will use the party’s Eastern Region conference today to reassert his authority with an attack on council tax.

He will say: “Council tax will rise by at least 5 per cent next year alone. And by 2011 it will have risen by more than 120 per cent since Labour came to power, hitting hardest those who have least. It is high time we moved to fair local taxation based on the ability to pay.

“Let me make this prediction: at the next election, the unfairness of Britain’s council tax will be clearer than ever before. Our opponents will ignore it. They will pretend it doesn’t matter, but they do so at their peril. Because people are not stupid.

“Council tax is rising steadily to the top of the political debate. And without reform, Prime Minister, the council tax will be your poll tax.”

How cards may fall

How to trigger a leadership election Sir Menzies resigns, asks for an election, dies or is no longer an MP A majority of Liberal Democrat MPs vote in a motion of no confidence 75 local parties or other affiliated groups call for an election after a general meeting

Odds on Sir Menzies’s survival William Hill says that Sir Menzies is 6-4 to be gone by Christmas and 8-11 to be gone by next election

Bookies’ odds for Sir Menzies’s successor Nick Clegg 7-4 Chris Huhne 4-1 Charles Kennedy 8-1 Vince Cable, Sarah Teather 10-1 Julia Goldsworthy 14-1 Ed Davey 14-1 Nick Harvey, Michael Moore 16-1

Source: William Hill

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