Nick Clegg on the offensive over marriage tax breaks
Liberal Democrat leader Nick Clegg has said the idea of tax breaks for married couples is wrong, and would not work.
The deputy prime minister told Sky News there were "philosophical differences" with the Lib Dems' coalition partners, the Conservatives, over the issue.
He said there was a limit on what the state "should seek to do in organising people's private relationships".
Fellow Lib Dems Vince Cable and Simon Hughes also attacked the idea during interviews with the BBC.
Mr Hughes, deputy Lib Dem leader, also denied the issue showed coalition tensions, telling BBC Breakfast it was one of four areas in the coalition agreement where the two parties had agreed to differ.
The other areas were nuclear power, nuclear energy and tuition fees, he said.
Conservative leader David Cameron said in his party conference in October: "Marriage is not just a piece of paper. It pulls couples together through the ebb and flow of life.
"It gives children stability. And it says powerful things about what we should value. So yes, we will recognise marriage in the tax system."
Conservative backbenchers are pressing for their party's election pledge to introduce transferable tax allowances worth up to £150 a year to be implemented during the current parliament.
Mr Clegg told the Dermot Murnaghan programme he was in favour of marriage, but said children "thrived best when they see their parents happy together", whether they were married or not.
He said that he did not think the state offering people "20 quid back would make much difference to people's decisions" on whether or not to get married.
Business secretary Vince Cable told BBC One's Andrew Marr Show that he was a big believer in marriage personally, and also rejected the suggestion Mr Clegg had brought up the subject as a "gratuitous" bit of coalition politics.
Mr Clegg is due to expand on the subject in a speech on Monday to a think tank in London about the "open society".
"We should not take a particular version of the family institution, such as the 1950s model of suit-wearing, bread-winning dad and aproned, home-making mother - and try and preserve it in aspic," he will reportedly tell the Demos think-tank.
"That's why open society liberals and big society conservatives will take a different view on a tax break for marriage.
"We can all agree that strong relationships between parents are important, but not agree that the state should use the tax system to encourage a particular family form.
"Conservatives, by definition, tend to defend the status quo, embracing change reluctantly and often after the event."
But the Centre for Social Justice think-tank, which was founded by Conservative Work and Pensions Secretary Iain Duncan Smith, rejected Mr Clegg's analysis.
Executive director Gavin Poole said: "Nick Clegg's stance flies in the face of all the evidence, completely ignoring national and international data demonstrating how important marriage is to the health and well-being of children and families.
"Marriage is important because one in three couples who live together when a child is born split up before that child is five, compared to only one in 11 married couples."
Labour's deputy leader, Harriet Harman, said: "Despite Nick Clegg's attempt to spell out differences with the Tories, his actions tell a very different story.
"Whether it is trebling tuition fees, taking a backseat in Europe or giving up on electoral reform, it is clear that the Lib Dems have sacrificed their liberal traditions."