On the eve of the election of the new Labour leader, Conservatives launched an attack on the party’s financial policies, calling on whoever wins the race to succeed Gordon Brown to explain what cuts they would impose.

Tory backbencher Matthew Hancock released a dossier arguing that both David and Ed Miliband had made commitments during the leadership contest which would require cuts running into tens of billions of pounds.

Both of the front-runners for the leadership backed former chancellor Alistair Darling’s plan to halve the state deficit by the end of the Parliament, which Tories estimate would cost £44 billion, said Mr Hancock.

But he said that both had opposed coalition government measures to bring down the deficit, such as raising VAT to 20 per cent, cutting child trust funds and scrapping the Building Schools for the Future programme, while making unfunded spending promises.

David Miliband had committed himself to policies such as a National Care Service and the extension of the Future Jobs Fund, which would cost more than £22 billion, while setting out extra taxes which would raise only £11 billion, said Mr Hancock. This left the shadow foreign secretary needing to identify cuts worth £55 billion, said the West Suffolk MP.

And Mr Hancock said Ed Miliband’s promises, including the National Care Service and a £7-an-hour living wage, would cost more than £28 billion, with only £5 billion of additional revenues identified from taxes on banks, leaving him needing to detail £67 billion of cuts.

Mr Hancock said: “On the central question of our time – how to deal with the deficit – the next Labour leader has big questions to answer.

“Both Milibands were at the heart of the Labour government that left the country in such a mess, and have now accepted the need for cuts to deal with the record deficit.”