A senior Liberal Democrat has lifted the lid on Tory plans for an £8bn plan to cut welfare, including slashing child benefits and child tax credits.

Chief Secretary to the Treasury Danny Alexander reveals that in June 2012, members of the Quad – the inner group of the four most senior cabinet members – were sent a paper by the Work and Pensions Secretary Iain Duncan Smith entitled "Welfare Reform Quad Summer Reading Pack" setting out plans for £8bn of welfare reforms.

The Guardian reported that the proposed cuts included limiting support to two children in child benefit and child tax credit - cutting up to £3,500 from a family with three children.

The Tories also planned to remove the higher rate child benefit from the first child, an average cut of over £360 for every family with children. And means-testing child benefit would be introduced, cutting £1,750 for a two-child, middle-income family.

Child benefits would also be removed from from 16- to 19-year-olds – a cut of more than £1,000 for parents of a single child.

Alexander, in a statement setting out his reasons for disclosing the existence and content of the documents,said: "I am lifting the lid on this now because the Conservatives are trying to con the British people by keeping their planned cuts secret until after the election.

"It's clear from our time in government that the Tories target will be slashing support for families.

Danny Alexander
Liberal Democrat Danny Alexander posed outside of the Treasury with a yellow box. Getty

"They now ask the British people to trust them when they make unfunded pledges on health and tax yet they won't tell us how they will cut welfare for millions of families to pay for their plans. They may give with one hand but they will take away twice as much as with the other."

Another Lib Dem source told the paper: "The measures set out in the document would have raised over £8bn – and shines a light on the scale of the cuts to working age welfare support the Tories will need to make to deliver on their cuts to welfare.

"Whilst the Tories refuse to make their cuts public it is clear they have already done the thinking If this is what they were capable of proposing in 2012, this is what they will be planning in 2015. It's really important political leaders should be held to account on this in the last TV debate of the election. The public need the full picture to make the judgement."

Responding, Tories said this was "desperate stuff from Liberal Democrats", who were "now willing to say anything to try and get attention. We don't recognise any of these proposals and to be absolutely clear, they are definitely not our policy."