Lord Mandelson has blasted Labour for failing to have a strategy for decentralising power from London to northern England.
The former business secretary, a key figure in the governments of Tony Blair and Gordon Brown, accused his party of having "language, not policies" for rebalancing the country's economy and political system.
And he said that the lack of an alternative to Chancellor George Osborne's Northern Powerhouse had been a "huge political mistake".
Lord Mandelson told the BBC's Sunday Politics North West programme: "The Labour Party had positions or it had postures, or put it a different way, if I was going to be really cruel - it had language.
"It had language but I don't think it had the policies seriously to rebalance both the economy and the political system of this country.
"We were not radical enough in what we were proposing to decentralise and to devolve away from London and to the regions."
Lord Mandelson said that George Osborne had "got it" when it came to decentralisation, although he put it down to electoral calculation.
"He got an idea, whatever his motive was, and he is running with it and we let him do so and that was a huge political mistake," Lord Mandelson added.
Mr Osborne said last month that northern England would get more powers over housing, planning, transport and policing.