ED Miliband yesterday accepted Coalition spending cuts while simultaneously holding out the promise of radical change along the lines of the 1945 Attlee government if Labour is re-elected.

The apparently contradictory message emerged in an interview in which the Labour leader harked back to the post-war reforms of the British state, and a speech in which he said the party must face "hard reality" and endure Coalition austerity in order to be "credible" with voters.

This Wednesday, George Osborne will set out a further £11.5 billion of austerity cuts when he announces the 2015-16 spending round.

The Chancellor's first spending review since October 2010 will detail £740bn of spending across 17 Government departments.

With education, health and overseas aid – some 60% of department spending – ringfenced against cuts, the burden falls on other areas, such as welfare.

Instead of a 2.8% cut all round, unprotected departments must cut an average of 8% instead.

Osborne's last review, which cut overall spending by 19%, was supposed to fix the UK's troubled finances within a single parliament.

But lack of growth in the economy has forced him to extend the cuts another year, past the General Election due in May 2015.

In a speech to Labour's National Policy Forum in Birmingham, Miliband said Labour would not borrow to reverse the cuts if it won in 2015. "Nobody here should be under any illusions: the next Labour government will have to plan in 2015 for falling departmental spending.

"Our starting point for 2015-16 is that we won't be able to reverse the cuts in day-to-day current spending unless it is fully funded from savings elsewhere or extra revenue, not from more borrowing.

"So when George Osborne stands up next week and announces his cuts in day-to-day spending, we won't be able to promise now to reverse them because we've got to be absolutely crystal clear about where the money is coming from.

"We will show the discipline the challenge of our times demand. It is the only way we can credibly change our country. It's a hard reality.

"I am clear about it. [Shadow chancellor] Ed Balls is clear about it. And everyone in the Labour Party should be clear about it too."

Labour has already said it would end the winter-fuel allowance to better-off pensioners, and not reverse child-benefit cuts for households with someone earning over £50,000 a year.

In an interview published just before the speech, Miliband said high spending was not the only route to social justice, and that Clement Attlee's government had created the welfare state on a balanced budget.

Pledging to devolve more power to councils and stop developers hoarding land, he said: "If you go into the roots of the Labour party and think about our most dramatic, society-changing government, the 1945 government, we all remember the NHS, building homes, and the family allowance. Believe it or not, they were running a budget surplus. It shows a government can be remembered in difficult times for doing great things."

Conservative Party chairman Grant Shapps said: "Ed Miliband's refusal to admit that Labour spent and borrowed too much in government, and his call for more spending and borrowing now, shows he's too weak to stick to his promise not to spend and borrow more.

"He only offers more spending, more borrowing and more debt – the same old Labour approach that got us into this mess in the first place."

Stewart Hosie, the SNP Treasury spokesman, said it was "depressing" that Labour had signed up to Osborne's "chosen road of cuts, cuts and more cuts with a lost decade of austerity facing us all".