Media playback is unsupported on your device Media caption Nick Clegg: "Put us back in government"

Nick Clegg has warned "a lot of mud" will be thrown in the run-up to May's election and said the Lib Dems will stand up for "optimism, not division" in the face of attacks from rivals.

In his New Year message, the deputy prime minister said his party deserved credit for "stepping up to the plate" in 2010 to form a stable government.

Labour, he said, was still "in denial" about its economic legacy.

And the Conservatives, he claimed, had "swerved off to the right".

May's election will be the first time in many years that a Liberal party has gone into an election as a party of government and been judged on its record in power.

The Lib Dems are bracing themselves for what one senior party figure has called a "survival election" after suffering a series of humiliating by-election results in the past 18 months and being at risk of being outpolled by the Green Party, as well as UKIP.

'Grim choice'

But in his end-of-year message to activists, Mr Clegg said it was his political rivals who were offering a "pretty grim choice" and, in contrast, the Lib Dems had a positive agenda.

"I will always stand up for the Liberal British values of openness, tolerance and compassion against those who peddle the politics of grievance, fear and blame," he said.

"This year, a lot of mud will be thrown. A lot of over-the-top claims will be made, a lot of accusations will be hurled around the place. Ignore them. Make 2015 a year for hope, not fear. For optimism, not division. For everybody."

Mr Clegg has suggested that only his party's participation in another coalition government will guarantee that the economic recovery continues in a sustainable and fair direction.

'Volatile'

The Lib Dem leader, who opposes Tory plans for £30bn in spending cuts in the first years of the next Parliament to try and clear the £90bn deficit, said his current coalition partners would "look after their own kind" if they were in power on their own.

"Now that there's an election looming, far from sticking to the plan we've pursued in government, the Conservatives are swerving off to the right and advocating ideological cuts to our public services," he said.

And he said Labour was not credible on the economy, suggesting its leader Ed Miliband believed he could "wave a magic wand and everything will be better".

Lib Dem deputy leader Malcolm Bruce told the BBC there was a "very volatile" political mood in the country at the moment but he believed support for his party would "firm up" as the election approached.

"I am not prepared to allow punters or other people to tell people how they are going to vote until they actually vote," he told Radio 4's World at One programme.

"Our view is that there are people out there who have yet to make up their mind and when they reflect on the positive things that the Liberal Democrats have achieved, on tax, pensions, the green agenda and on schools, they actually want to see more, not fewer, Liberal Democrats in the next Parliament. That is what our campaign is going to be about."