'Conservatives are like a broken shopping trolley... they keep veering off to the right': Clegg launches savage attack on Tories Lib Dem leader uses his keynote speech at his party's spring conference to claim the Eastleigh by-election proves his critics wrong Nick Clegg today launched a major attack on David Cameron and the Conservatives, claiming his coalition partners are like a 'broken shopping trolley' which keeps drifting to the right. In a bombastic speech which defied his party's woeful ratings in the opinion polls, the Lib Dem leader boasted that last month's Eastleigh by-election proved they could win against the Tories. And he tore into Theresa May, who has emerged as a Tory leader-in-waiting, flatly rejecting her call for Britain to pull out of the European Convention on Human Rights. Lib Dem leader Nick Clegg used his conference speech in Brighton to attack the Tories and insist his party can still win The Lib Dem leader used his keynote speech at the party's spring conference in Brighton to issue a rallying cry to activists to go on the offensive against the Conservatives. 'The Conservatives, on their own, will never deliver the fairer society - it's just not who they are,' he told delegates. Take the mansion tax. Even now, when millions of families are feeling the pinch, they still refuse to ask people who live in multi-million pound homes to chip in a bit more. 'The Conservative party knows it needs to stay on the centre ground to have any chance of speaking to ordinary people's concerns. 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. Mr Clegg told delegates the Lib Dems were no longer a party of protest, and singled out Home Secretary Theresa May for criticism The Lib Dems are plotting to use Tory disarray over Europe and the rise of the UK Independence Party to win seats from their coalition partners. Lib Dem strategists believe they can "pinch" seats from the Conservatives as David Cameron haemorrhages support to UKIP, despite languishing on just eight per cent in the latest polls. Mrs May, the Home Secretary, yesterday gave an extraordinary speech ranging far beyond her law and order brief which was seen as a pitch for the Tory leadership if Mr Cameron is forced to stand aside. In a move designed to appeal to Tory traditionalists, she said it was time to stop criminals getting off scot-free because of human rights laws, she said, declaring: "All options - including leaving the ECHR altogether - should be on the table." But Mr Clegg singled her out as the only Tory minister named for criticism, flatly rejecting the idea that the coalition would even consider quitting the ECHR. Mr Clegg sought to shake off weeks of bad headlines over the Lord Rennard scandal and Chris Huhne's conviction to convince the Lib Dems they can still 'win' Mr Clegg began his day with a visit to a creche for children of party members He said: 'The Conservatives would actively take away rights enjoyed by British citizens just to appease their backbenchers. 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. Make no mistake, 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. Mr Clegg declared the Lib Dems are no longer a "party of protest" and claimed public rows with Tories have helped to define his party's identity. Home Secretary Theresa May used a wide-ranging speech to cement her position as a possible Tory leader-in-waiting Mr Clegg claimed "political obituaries" predicting the wipeout of the Lib Dems had been premature, hailing the party's victory in the Eastleigh by-election as proof that they can win while being the junior partner in a coalition. Nick Clegg suffered an embarrasing defeat at the hands of his activists as the Lib Dem conference overwhelmingly rejected so-called secret courts legislation. Delegates ordered their MPs and peers to oppose the plans, saying they were contrary to 'core' Lib Dem values. Lawyer Jo Shaw announced in the hall that she was resigning her membership in protest - joining human rights barrister Dinah Rose QC who has also quit. The row came despite Mr Clegg defending his handling of the issue in a bad-tempered question and answer session last night. The Justice and Security Bill was given its third reading in the Commons last week, but saw a rebellion from some Tories and Lib Dem MPs. In his speech today, Mr Clegg claimed last month's by-election campaign is proof the Lib Dems can win against the Tories. Yet we still won," he said. The leadership has been eager to use the gathering to move on from damaging allegations of sexual harassment by Lord Rennard - which he denies - and the conviction of former Cabinet minister Chris Huhne. MailOnline revealed yesterday that Mr Clegg has begun a purge of scandal-hit Liberal Democrats in a bid to clean up his party's tarnished image. Mr Clegg conceded that some Lib Dems had harboured "quiet fears" that coalition would do irreparable damage to the party. But he insisted that the risk can pay off at local elections in May and the next general election in 2015. The idea that, in Tory facing seats the Liberal Democrats will find it impossible to distinguish our record, our values, from theirs," Mr Clegg said. 'We don't lose our identity by governing with the Conservatives. A new opinion poll puts UKIP just 10 points behind the Conservatives. The Opinium survey for the Observer showed Labour on 39 per cent, the Tories on 27 per cent and UKIP on 17. The Lib Dems are down on eight per cent. UKIP beat the Tories in the Eastleigh by-election, leading ministers to quickly dismiss the rise of Nigel Farage's party as a protest vote'. Mr Clegg said the Lib Dems have shed their own reputation as a party of protest. In the days after the by-election, even though we won, I was asked how I feel about our party no longer being a magnet for the protest vote. Business Secretary Vince Cable, pictured with wife Rachel Smith, has warned against deeper spending cuts to his budget which he said would damage industry Lib Dem MPs will come under intense pressure to side with Labour this week as Ed Miliband forces a Commons vote on the party's dream of imposing a "mansion tax" on the better off. Labour has drawn up a Commons motion voicing support for the idea of a mansion tax on homes worth more than £2 million. The vote, just a week before the Budget, will force Lib Dem MPs to choose between one of their most cherished policies and the official Coalition stance, which is against a mansion tax. But Mr Clegg hinted that his party may not join Labour in the vote. Attacking Mr Miliband;s prty, he said: 'First they destroy the economy. They spend all the money. They leave us with nothing. Then they oppose every single saving the Coalition has been forced to make with not a single suggestion for how to raise money instead. Then they finally do come up with an idea. And it's brilliant. But it's the Mansion Tax - and we came up with it first. Labour are embracing opposition in the worst possible way. All they are interested in is striking poses and playing parliamentary games. Mr Clegg earlier met young activists and new Lib Dem MP Mike Thorrnton On the eve of the conference Business Secretary Vince Cable raised the prospect of increasing borrowing to fund big money infrastructure projects. But Mr Clegg has rejected the idea. He said: 'Let no one tell you that this Government isn't straining every sinew to invest every available pound into UK infrastructure. We will and must do more to mobilise investment into our long-term infrastructure needs. I agree with that. Vince agrees with that. Danny agrees with that. But, as we all equally acknowledge, there are no cost-free, risk-free ways of finding such huge sums of money. Not at a time when Labour left the cupboard bare and we still have the second highest deficit in Europe, behind only Greece. Ours is a growth strategy guided by liberal pragmatism from a Coalition government anchored firmly in the centre ground. The deficit down by a quarter. Fixing our banks. A million jobs created in the private sector. Money back in people's pockets. A stronger economy, a fairer society, enabling everyone to get on in life.