Mr Peter Mandelson says he believes his political career was scuppered by clashes with the Left during his years helping to create New Labour.
The one-time Northern Ireland Secretary said he wished he had made fewer enemies when he worked as Labour's director of communications.
He said he was left without "the political base that any politician requires.
"I didn't think ahead. I didn't think that one day I would be a politician standing in my own right needing support," he told this morning's Guardiannewspaper. "In pure political terms that was a failing".
Mr Mandelson says the "baggage" he carried from his past and his close relationship with Mr Balir meant he had to "doubly justify, doubly perform" when he became a minister.
He was forced to resign as Northern Ireland secretary last January over his alleged role in the Hinduja passports affair. He quit as Trade and Industry Secretary over a controversial £373,000 home loan from Geoffrey Robinson, then paymaster general.
The Hartlepool MP says he does not harbour any hopes of a third chance at ministerial office.
Mr Mandleson said he was "happy, but not fulfilled. I enjoy my life but I am under-stretched". He also revealed his social life had suffered since his resignation. "Nobody invites me any more".
PA