Hamas’s attack on October 7 impacted Sir Keir Starmer’s wife’s family in Israel, the Labour leader has said for the first time.

Predicted to become the next Prime Minister after the July 4 general election, Sir Keir told the Guardian this weekend: “Half of the family are Jewish, they’re either here or in Israel.”

Speaking about October 7, Sir Keir said “Thank God” nobody was directly affected by the massacre, but added that there was “no doubt" his family in Israel had been affected by the war.

The Labour leader told journalist Charlotte Edwardes that his wife, Lady Victoria Starmer, and their two children are not Jewish according to Lady Victoria’s father’s family.

“No, no, they’re not Jewish for reasons I won’t bore you with. Bernard’s dad’s family didn’t accept that.”

The comment appeared to suggest an Orthodox definition of Judaism and hinted at historical issues around his Jewish father-in-law Bernard Alexander’s marriage to his late wife Barbara, who converted to Judaism.

The Starmer family belongs to London's Liberal Jewish Synagogue in St John’s Wood.

They say kiddush regularly. “Pretty much every week” there’s a challah, Sir Keir said, adding that sometimes his wife's family come over to their north London home for Shabbat, or Lady Victoria’s sister joins them on Zoom.

The Labour leader has two children with his wife. In 2020, he said they were “bringing [the children] up to recognise the faith of part of their grandfather’s family, and it’s very important.”

“Just carving out that tradition, that bit of faith on Friday is incredibly important, because we get together and we do Zoom prayers now.”

This week he reaffirmed how important their Jewish heritage is, “We’re very keen for the children to know about it, to understand it. Half of the family are Jewish, they’re either here or in Israel.”

In the days after the massacre in October, Starmer told LBC that he and his wife “have a deep sense of shock at what is happening”. He went on: “I’ve never known a time of such incredible anxiety”.