Meg Hillier has said Jeremy Corbyn has yet to "convince" Labour Party members he could hold the role of Prime Minister.
The Labour MP for Hackney South and Shoreditch said the party leader first had to "step up" and tackle alleged Labour antisemitism, amid criticisms of his handling of complaints.
"I think he really needs to show his mettle if he wants to convince all of us he is ready for that job," Ms Hillier said.
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"It is really important he shows leadership and strength in tackling that [antisemitism]."
Last week, eight Labour MPs left the party to join the Independent Group, with many - including Jewish MP Luciana Berger - citing antisemitism as their reason for defecting.
'I've known him for 25 years'
Meg Hillier MP. Image: UK Parliament
"I have known him [Corbyn] for 25 years and I know that when he wants to he can speak firmly about things," Ms Hillier said.
"That's one example of where he needs to step up if he wants to demonstrate, not just to our party, but the country that he's ready to walk into Number 10 Downing Street.
She added: "The fact that this has been rumbling on for two years isn't good,"