A senior Coalition minister has courted controversy by suggesting benefits should be capped once families have two children.

Within hours, the comments by Iain Duncan Smith, the Work and Pensions Secretary, were disowned by the LibDems.

A source close to Nick Clegg said the party was "not keen" on the suggestion, which he said would not even save much money.

Mr Duncan Smith also faced criticism for snubbing an invitation to appear ata Holyrood committee, saying the issue of welfare was reserved to Westminster.

Earlier, the former Tory leader said it was "madness" that taxpayers subsidised poor families to have large numbers of children.

Once a couple had too many offspring their benefits should be capped, he said, and suggested the cut-off might be two children.

Mr Duncan Smith is under pressure to find another £10 billion of cuts.

He said those on middle incomes tended to have fewer offspring because they had to think about how they could afford them.

"In other words, the problem for those who are paying the taxes, paying the bills – they make the decisions about their lives, even if they sometimes would like to maybe have extra children, they make decisions," he said. "People who are having support through welfare are often free from that decision."