Lord Mandelson questioned Mr Osborne's credibility
Conservative claims that the party is a progressive force in politics are "rank hypocrisy", Business Secretary Lord Mandelson has said.
He also said shadow chancellor George Osborne's plans to reform health and education would mean spending cuts.
This could result in no "safety net" for millions of people, he added.
But Lord Mandelson told BBC Radio 4's Today programme that social mobility was "not getting better as quickly as we originally wanted to see".
The peer's attack came as he is deputising for Prime Minister Gordon Brown, who is on holiday.
In a speech on Tuesday, Mr Osborne said Labour had "abandoned the field of progressive politics" to the Tories and predicted the party would be "condemned to irrelevancy for many years to come".
He attacked the government for running up "huge national debts that future generations are left having to pay for".
Mr Osborne said the UK should be more like Sweden, where improvements had been made in education while balancing the books, by bringing more private providers into the state sector.
But Lord Mandelson, who has had several run-ins with Mr Osborne previously, told Today that the public sector savings "the Tories envisage will not produce a better service".
He added that cuts would "leave no safety net for those who cannot afford to go private".
Lord Mandelson also said: "This exposes the rank hypocrisy of George Osborne's claims to represent the party of progressives. I've never heard anything so laughable in my life."