Nick Clegg is planning to promise tax cuts, free childcare and benefit curbs for foreign workers who cannot speak English at the general election, according to leaked documents.

Details of the Liberal Democrats' manifesto proposals were embarrassingly photographed in the hands of his strategy adviser Ryan Coetzee outside the Scotland Office in Whitehall.

The draft had four "red lines" for any coalition negotiations, including a pledge to "balance the Budget by 2018" - two years earlier than Labour's deadline.

There is a pledge to raise the income tax threshold to £12,500 by 2020 by increasing taxes on the rich.

The manifesto also makes other promises on mental health and education.

"Only the Liberal Democrats will create the opportunity for everyone by building a stronger economy and a fairer society," the draft states.

It also indicates a tougher line on immigration. The LibDems said the tone of the document should not surprise anyone.