Nick Clegg has mocked the Conservative Party, saying his coalition partners are "like a broken shopping trolley" that keeps lurching to the right.
The Lib Dem leader also poked fun at the Tory candidate in the Eastleigh by-election, saying David Cameron was relieved she had lost.
In his keynote speech at the party spring conference in Brighton, the Deputy Prime Minister warned the Conservatives that he would never agree to quitting the European Court of Human Rights.
And he claimed that despite the polls Lib Dems would benefit from having been in coalition - because voters would be able to spot the differences with the Tories.
He told activists: "The longer you stand side-by-side with your opponents, the easier your differences are to see.
"We don't lose our identity by governing with the Conservatives. The comparison helps the British people understand who we are."
And it came just after activists voted to reject controversial plans for secret courts.
Clegg hit out at Tory voices attempting to push the Prime Minister to the right, saying his coalition partners were delivering "bizarre mixed messages".
He singled out Home Secretary Theresa May - touted by some as a successor to Mr Cameron - for suggesting Britain could leave the European Convention on Human Rights.
"The Conservative party knows it needs to stay on the centre ground to have any chance of speaking to ordinary people's concerns," he said.
"At least the leadership seem to. But they 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...
"Yesterday Theresa May made a speech arguing the option of leaving the Convention should remain 'on the table'.
"Well, I tell you, it won't be on the Cabinet table so long as I'm sitting round it."
He criticised both main parties, saying the Tories could not be trusted with society, and Labour couldn't be trusted on the economy, repeating an attack line first used in January that is likely to feature heavily in the 2015 campaign.
Clegg hailed the Lib Dem victory in the Eastleigh by-election, claiming this was because, not in spite of, the party being in power.
And the activists enjoyed a joke about outspoken Tory candidate Maria Hutchings, who trailed behind UKIP in third place.
Clegg said he had been asked by David Cameron to pass on "sincere thanks" for preventing her from becoming a Tory MP.