Tony Blair has promised to help “millions of effectively politically homeless people”, calling Labour leader Jeremy Corbyn a man of “the far left”.
The former prime minister said the state of UK politics “dismayed him”.
But he ruled out any return to “frontline” action, telling New Statesman magazine the media would “move to destroy mode”.
Meanwhile, Sir John Major, another former PM, urged the “solid centre” to speak out against “extremes”.
There has been speculation that Mr Blair, who won three general elections for Labour, will make a return to mainstream politics, having mostly avoided the limelight since leaving Downing Street after 10 years as prime minister in 2007.
This speculation increased when he announced he was closing most of his commercial operations to focus on philanthropic work.
He has also said the public faces a choice between a government pursuing a “hard Brexit” and an “ultra-left” Labour Party with out-of-date policies.
‘Too much hostility’
But Mr Blair told the New Statesman “what I’m doing is to spend more time not in the frontline of politics, because I have no intention of going back to the frontline of politics”, rather he was “trying to create the space for a political debate about where modern Western democracies go and where the progressive forces particularly find their place”.
He said: “I’m dismayed by the state of Western politics, but also incredibly motivated by it. I think, in Britain today, you’ve got millions of effectively politically homeless people.”
Mr Blair added: “I can’t come into frontline politics. There’s just too much hostility, and also there are elements of the media who would literally move to destroy mode if I tried to do that.”
He denied reports that he had called Theresa May a “lightweight”, describing the prime minister instead as “a very solid, sensible person” who had a very difficult hand to play.
And, on Mr Corbyn, Labour’s leader since last year, he said: “I did not call Jeremy Corbyn ‘a nutter’. I don’t think he’s a nutter. I just think he is someone on the far left of politics and he’s been consistent for the last 35 years that I’ve known him, which is fine.”
Meanwhile, speaking at a dinner in Westminster on Wednesday, Sir John Major, Conservative Prime Minister from 1990 to 1997, called for the 48% of people who voted against Brexit in June’s referendum to have their views considered.
“The tyranny of the majority has never applied in a democracy and it should not apply in this particular democracy,” he said, according to former BBC parliamentary correspondent Robert Orchard, who attended the event.
Sir John argued that Parliament would have to ratify whatever deal was finally reached by the Brexit negotiators and there could then be a case for a second referendum, depending on the deal on offer.
He said: “We need to lift our eyes away from the philosophical dislike that some people feel for Europe and towards the practical implications of what our government must negotiate in the next few years.”
Sir John added: “In an age when the extremes of politics are rising, the solid centre of opinion should speak out for our values, for our future, and all that is good about our society. Now is not the time for silence… we should speak out.”