A newly optimistic Nick Clegg, following the party's success in the Eastleigh byelection, said the Liberal Democrats have moved from being a protest party to the anchor that will deliver centre-ground governments committed to both a strong economy and a fairer society.
Closing his party's spring conference in Brighton, he also insisted that being in a coalition government did not dilute the party's identity, but strengthened it.
He said: "There is a myth that governing together, in coalition, diminishes the ability of the smaller party to beat the bigger party."
Clegg has been armed with a barrage of new polling material setting out the centrist themes he needs to pursue to claw his party back to around 20% by polling day, a base from which the party could again hold the balance of power.
He said the Eastleigh result had utterly confounded those who had argued in "Tory facing seats" that the Lib Dem party would be unable to distinguish its record and values from those of the Conservatives.
"The longer you stand side by side with your opponents, the easier your differences are to see," said Clegg. "We don't lose our identity by governing with the Conservatives. The comparison helps the British people understand who we are."
Party managers admitted the conference – against the backdrop of sex allegations against the party's chief executive Lord Rennard and a grim trial involving former cabinet minister Chris Huhne – could have been a disaster if Huhne's old Eastleigh seat had been lost in the byelection.
A poll of UK-wide marginals, commissioned by Lord Ashcroft and published on Saturday, showed the party losing 40 of its 57 seats. Officials said that, but for Eastleigh, the poll would have generated stories of a Clegg-led wipeout.
Instead, a confident Clegg was able to use his speech to attack his coalition partners, saying the Tory leadership knows it needs to stay on the centre ground to have any chance of speaking to ordinary people's concerns.
He said the leadership "just can't manage it, no matter how hard they try. They're like a kind of broken shopping trolley. Every time you try and push them straight ahead they veer off to the right-hand side."
He warned Theresa May, the home secretary, that as long as he remained around the cabinet table, he would not allow the proposal of British withdrawal from the European convention on human rights.
The bulk of his speech was taken up with his claim that only his party can make the combined centrist offer of a strong economy and a fair society, asserting the Tories provide only the former and Labour only the latter.
The Lib Dems' new strategist, the South African Ryan Coetzee, has been responsible for detailed polling around the issues on which the party needs a stronger identity, notably the economy.
Coetzee's catchphrase is "On message. In volume. Over time," suggesting he is to try to impose some message discipline on the notoriously wayward Lib Dems.
Clegg told the conference he relished the fact that the party was no longer seen as the party of protest, or the automatic "none-of-the-above" choice.
"The Liberal Democrats are not a party of protest, we are a party of change. A party that is for things, not simply against things. A successful political party cannot thrive just by picking up the votes that have been lost by its opponents. Our ambition is to reach out to the millions of people in this country who want a party that strikes the right balance between economic credibility and social fairness."
In a thinly coded reference to Ukip, he added: "We are not some kind of receptacle for people who don't like the world – and don't want to do anything about it. We grapple with the world. We strive to make it better." But However, Clegg will shortly make his own intervention on immigration.
With the business secretary Vince Cable saying the balance of risk had begun to shift in favour of economic stimulus, Clegg said: "Britain's economic recovery has proved more challenging than anyone imagined. The crash in 2008, deeper and more profound than we knew."
But he also warned of the dangers still confronting the economy and the threat of rising interest rates, saying: "Just two weeks ago, the uncertain outcome of the Italian election threatened to plunge Europe back into crisis. Suddenly we were reminded of the danger that looms when markets question the ability of governments to live within their means.
"Countries around the world face the same hard truth: we must all pay the piper in the end. I want to make one thing clear: we will not flinch on the deficit.
"But to be unflinching is not to be unthinking. And the idea that the choice is between a cruel and unbending plan A and a mythical plan B is simply not the case.
"When economic circumstances around us deteriorated and UK growth forecasts suffered, voices on the right called for us to respond by cutting further and faster. But instead we took the pragmatic choice to extend the deficit reduction timetable. As tax receipts went down we let the automatic ebb and flow of government borrowing fill the gap."
Clegg denied the coalition was slashing the state, saying: "By the end of this parliament, public spending will still be 42% of GDP. That's higher than at any time between 1995 and when the banks crashed, in 2008."
He promised "no matter what the issue – safeguarding the NHS, creating green jobs, stopping profit-making in schools, preventing a return to two-tier O-levels – the Liberal Democrats will keep the coalition firmly anchored in the centre ground."
Clegg went on to criticise Labour for opposing "every single saving the coalition has been forced to make with not a single suggestion for how to raise money instead".
Clegg continued: "By now I expected a re-energised Labour party, refocused. The whole point of opposition parties is that they come up with ideas. But they haven't. Under Ed Miliband and Ed Balls, Labour remain a blank page in British politics."
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image: © Liberal Democrats