Jeremy Corbyn has accused Theresa May of being "insecure" about her authority - and retreating into a "presidential bunker mentality" reminiscent of Tony Blair.
The Labour leader said he believed in "empowering others to make up their minds and come on board when they are ready", while the Prime Minister was obsessed with stifling dissent.
Mr Corbyn said Tony Blair's premiership showed what can go wrong if leaders go unchallenged.
Speaking to an audience of supporters in London's East End, he said he recognised similar characteristics in Mrs May.
He said: "It taught me that if leaders go unchallenged, they can make some of the most damaging mistakes.
"And if party leaders put themselves ahead of serving the people, they stop listening and even put our country at risk.
"Barely nine months into Theresa May's premiership, there are clear warning signs that she and her closest advisers are slipping into that presidential bunker mentality.
"Whereas it is the job of leadership to hold open the space for dissent, new thinking and fit-for-purpose policy.
"So while it might not be the stuff of soundbites, I have always believed in standing firm and empowering others to make up their minds and come on board when they are ready.
"It is the mindset that gets community centres and nurseries built, and increasingly defends them from closure.
"It is the mindset that negotiates hard for better conditions in the workplace. It is the mindset that serves the many, not the few."
Mr Corbyn said he had previously thought political leaders had no choice but to give in to "vested interests" while manipulating the public.
"I didn't want to be like that. And it wasn't clear to me there could be another way," he said.
"But I've learned there is. Whereas insecure leaders want to feel stronger by asking you to give them more power, I recognise strong leadership as equipping you with more power."