Keir Starmer has predicted that Angela Rayner will return to the cabinet, calling his former deputy, who resigned in September after underpaying stamp duty on a property purchase, “hugely talented”.

In an interview with the Observer, the prime minister described Rayner, who left school aged 16 without any qualifications, as “the best social mobility story this country has ever seen”.

Rayner resigned as deputy prime minister and housing secretary after Starmer’s ethics adviser, Sir Laurie Magnus, found she had breached the ministerial code over her underpayment of stamp duty on a flat in Hove.

Magnus said Rayner had “acted with integrity” but that her failure to get sufficient advice on how much stamp duty she had to pay amounted to a breach of the code.

Asked in the interview if he missed Rayner, Starmer replied: “Yes, of course I do. I was really sad that we lost her. As I said to her at the time, she’s going to be a major voice in the Labour movement.” Asked if she would return to cabinet, the PM said: “Yes. She’s hugely talented.”

That is more definitive than anything Starmer has previously said, even if an imminent return would be complicated by the finding that she had breached the ministerial code.

In his letter in September in response to Rayner’s resignation, Starmer did not say he expected her to return, writing: “Even though you won’t be part of the government, you will remain a major figure in our party.”

This was in contrast to his letter in January to Tulip Siddiq, who resigned as a Treasury minister over controversy about her close ties to her aunt, the ousted prime minister of Bangladesh since accused of corruption.

Writing to Siddiq, Starmer was explicit that “the door remains open” for her to return to the frontbench.

Rayner has kept a low profile since her departure. She had been expected to table an amendment to the workers’ rights bill she spearheaded in government to speed up how quickly protections come into force, but dropped the idea after conversations with the business secretary, Peter Kyle.

Rayner is among a series of ministers who have been linked to speculation about possible efforts to remove Starmer, particularly if Labour performs badly in May’s Scottish, Welsh and local English elections. Her allies have rejected this.

In his Observer interview, Starmer said he believed Rayner and the chancellor, Rachel Reeves, faced misogyny. “All politicians get quite a lot of abuse these days but for women it’s always worse,” he said.