At Labour’s manifesto meeting on 11 May, there was one exchange that dominated the conversation as participants left. Angela Rayner, the shadow education secretary, had challenged John McDonnell, the shadow chancellor and Jeremy Corbyn’s longtime ally, over the draft document. In her broad northern tones, Rayner expressed dismay at the lack of attention for child protection and early-years funding.

“She wasn’t very pleased that there was more on protecting animals than children in the manifesto,” I was told. While early-years funding benefits the neediest, McDonnell’s focus had been on abolishing university tuition fees, which would benefit undergraduates, and thus middle-class families.

After a side meeting – the only one held with a shadow cabinet minister – the dispute was resolved. McDonnell later talked down the disagreement and declared that Rayner would be the “Nye Bevan of the Jeremy Corbyn government”. Not for the first time, Rayner had demonstrated her independence.

Although the 37-year-old did not join the rebellion against Corbyn, she has differentiated herself from the party leadership. The day before the manifesto meeting, she made a speech in which she praised Tony Blair despite the Corbyn team’s misgivings. “We’re going to see a generation of our children being held back,” she warned about the Tories’ plans. “It never used to be like this under Labour . . . Tony Blair spoke of the need to build an education system fit for a new millennium.”

When Blair entered office in May 1997, the red-haired Rayner had recently turned 17. She had left school the previous year, with no qualifications, after becoming pregnant.

Raised on a council estate in Stockport by a mother who could not read or write, “I wasn’t school-ready,” Rayner said recently. “Books weren’t a thing in my house. Mum couldn’t help me with homework.”

It was a signature New Labour achievement – Sure Start – that “rescued” Rayner. “Some may argue I was not a great role model for young people,” she said in her first party conference speech. “The direction of my life was already set. But something happened. Labour’s Sure Start centres gave me and my friends, and our children [she now has three], the support we needed to grow and develop.”

Rayner’s personal experience and her knowledge of her brief prompted her intervention at the manifesto meeting. Research shows that it is during a child’s earliest years, rather than secondary or higher education, that funding can make the greatest difference.

Her route into Labour politics was a familiar one. After becoming one of the youngest careworkers on the staff of Stockport council, she was elected as a Unison representative. She originally “didn’t know what a trade union was” but Rayner was encouraged by colleagues, impressed by her harrying of management. After becoming Unison’s most senior official in the north-west, she was elected in 2015 as the first female MP for Ashton-under-Lyne.

“I lay claim to being the only member of this house to have ever worked as a home carer,” she said in her maiden speech to the Commons. “Perhaps, too, I’m the only member of the house who, at age 16 and pregnant, was told in no uncertain terms I’d never amount to anything. If only they could see me now.”

After the party’s June 2016 crisis in which 63 frontbenchers resigned, she was promoted from shadow pensions minister to shadow for women and equalities. A week later, she became the youngest-ever shadow education secretary after the resignation of Pat Glass (who lasted 50 hours in the post).

It has proved the right brief for Rayner. Theresa May’s support for new grammar schools has united Labour in opposition, allowing Rayner to build alliances across the party and exploit Tory divisions. In the Commons on 12 September 2016, she told the Conservatives to “stop your silly class war”. As Tory MPs jeered, she remarked that it was the reply David Cameron gave in 2006 when asked what he would say to any backbencher who supported grammars.

Rayner has spoken of how her accent and appearance have led her to be “underestimated” (one email labelled her “as thick as mince”); she now uses this to her advantage. “A lot of better-educated people have come off worse against her,” an ally told me, citing a Channel 4 News exchange with Michael Gove.

Though loyal to Corbyn, Rayner has cast herself as non-factional. “Ideology never put food on my table,” she said in January this year. “I talk about Tony Blair’s tenure because it changed my life.”

Among Labour politicians, Rayner, whose journey is recognised as remarkable, is increasingly spoken of as a future leader. “She’s very ambitious,” a source said. “A leader of the party in the future? Who knows,” Rayner said of herself in February. This council estate girl, one senses, is determined to keep defying expectations.