Diane Abbott has said she advised her longtime friend Jeremy Corbyn not to launch a new political party because she believed it would struggle to make inroads under the first-past-the-post system.

Abbott, the MP for Hackney North and Stoke Newington, said last month she would not be leaving Labour in favour of Corbyn’s as yet unnamed party, despite the pair having worked closely together in the past.

Speaking at the Edinburgh international book festival in conversation with the campaigner and commentator Talat Yaqoob, Abbott confirmed she had spoken to Corbyn before the party’s launch to warn him against it.

“There were people around Jeremy encouraging him to set up a new party and I told him not to,” she said. “It’s very difficult under the first-past-the-post system for a new party to absolutely win. If it wasn’t first past the post then you can see how a new party could come through, but I understand why he did it.”

Abbott described Zarah Sultana, the independent MP launching the new party with Corbyn, as a “lovely person who is full of energy”. She said the party could get votes and support from people who were “not necessarily leftwing” but were “disappointed about the way [Labour has] gone in the past year”.

Abbott, who as the longest-serving female MP has the honorary title of mother of the house, is suspended by Labour. She lost the party whip in April 2023 after she wrote a letter to the Observer in which she argued that Jewish, Irish and Traveller people did not experience racism in the same way as Black people and likened their experience to that of people with red hair.

She said the letter published was a draft version and that her comments had been taken out of context. She was readmitted to the party in time to hold her seat at the general election. But she was suspended again last month after telling the BBC in an interview that she did not regret the remarks.

Abbott said in Edinburgh: “I think she and Jeremy are a great combination but at this point in time, it’s difficult to see how a brand new party wins. However, I think Jeremy’s party is going to do a lot better than people think, because a lot of people are not necessarily terribly leftwing. People are a tiny bit disappointed about the way we’ve gone in the past year.”

Asked whether she thought she would ever be accepted at the heart of the Labour party, Abbott said: “I think I am at the heart of the Labour party, it’s other people who aren’t.”

She was speaking at the festival about her book A Woman Like Me, during which she also said Keir Starmer had been “timid on Gaza” and that the proscription of Palestine Action was “absolutely dreadful”.