Keir Starmer's preferred candidate is behind rival Lucy Powell among members, who will decide the contest to replace Angela Rayner, poll suggests

Labour deputy leadership contender Bridget Phillipson has branded the controversial two child benefit cap "spiteful", as she tries to revive her stumbling campaign.

The education secretary, Keir Starmer's preferred candidate, also claimed its abolition was "on the table", months after Labour MPs were suspended from the party for voting for it to be scrapped.

But dumping the policy would cost about £3.5bn a year at a time when soaring borrowing figures have led to warnings that tax rises in November's Budget now look "inevitable".

Polls suggest Ms Phillipson is behind her opponent Lucy Powell, who Sir Keir sacked earlier this month, amid high dissatisfaction within the party leadership.

The limit had "punished and pushed children into hardship" and if she became deputy leader she would have a mandate to make tackling child poverty the government's "unbreakable moral mission", Ms Phillipson said in an interview with the Guardian.

More than 1 million children in working families are set to be affected by the policy, new analysis recently revealed, as Labour faces renewed pressure to scrap it.

Despite having at least one parent in work, thousands of families are struggling to afford the essentials as key benefits don't extend to their third child or beyond, a report by the Child Poverty Action Group (CPAG) has found.

The cap, introduced under Conservative welfare reforms, blocks parents from claiming the child element of universal credit worth £292.81 a month for a third or subsequent child born after April 2017.

Ms Phillipson said the issue was "profoundly personal" to her because she knew "the sting of growing up in poverty" in Tyne and Wear, where her house had damp problems and no heating upstairs.

She said that one winter, a neighbour pushed an envelope with money through the letterbox. It read: "For Bridget's coat."

"Lifting more children out of poverty is why I came into politics," she said. "I'm thinking every day about how to turn the tide on child poverty. Everything is on the table, including removing the two-child limit.

"I want the mandate to go further. The mandate, as deputy leader, to make tackling child poverty the unbreakable moral mission of this Labour government."

She added: "We should never forget that it was the Conservatives who introduced the two-child cap, a spiteful attack on children who were punished and pushed into hardship through no fault of their own. I have said time and again that a Labour government would never have implemented it."

Ms Phillipson is the co-chair of the government's child poverty taskforce, which is due to publish its findings this autumn.

Gordon Brown, who has condemned the two-child limit as "cruel", last month called for higher taxes on the gambling industry to scrap the cap.

Ms Powell has said ministers should clearly endorse the principle of scrapping the cap, saying it was the "single biggest policy we could do to address child poverty".

With Downing Street's backing, Ms Phillipson emerged as the frontrunner among MPs with the support of 175 to Ms Powell's 117. But a poll by Survation for the LabourList website this week put Ms Powell ahead with the party grassroots who will decide the contest, on 47 per cent to 30 per cent.

Phillipson bids to revive Labour deputy bid with two child benefit cap call