Sir Keir Starmer’s Government is facing further calls to scrap the two-child benefit cap, as MPs claim it would lift hundreds of thousands of children out of poverty.

Labour has faced consistent pressure to scrap the limit since before the election, from charities and its own backbenchers.

MP John McDonnell said the legislation put in place by the Tories is an “attack on the poorest” and argued that his party should plan to abolish the policy “within weeks”.

Meanwhile, SNP Westminster leader Stephen Flynn said he was “disappointed” that getting rid of the “heinous” cap did not feature in the King’s Speech.

With more than four million children now living in low-income households, the Government has committed to a ministerial taskforce to begin work on the child poverty strategy.

On Wednesday, Mr McDonnell told the Commons: “There is a simple act and we all know it, there is one simple act that could lift 300,000 children out of poverty this month, and it would be the scrapping of the two-child limit.

“I was in this House when the Tories introduced it, it was introduced as part of the stigmatising of all those on benefits.

“I did a speech, I actually think I said I’d swim through vomit to vote against this piece of legislation, and some of the nauseous speeches from the Tories at the time almost meant I would have to.

“It was an appalling form of attack on the poorest within our communities. I think we just need to lift that stigma, lift that impact, but we need to do it quickly.

“So, yes, set up this taskforce by all means, but produce a timetable that within weeks we will scrap the two-child limit.

“The argument is that: can we afford it? And will it be within our fiscal rules? Many of you will know over these last few weeks the OBR (Office for Budget Responsibility) have lifted and revised its growth figures upwards, the IMF (International Monetary Fund) has dramatically increased the growth figures upwards.”

Mr McDonnell (Hayes and Harlington) added that “the resources are there” and appealed to the Government to “take the benefits” of the growing economy and scrap the policy.

Earlier in the session, Mr Flynn confirmed his party had mooted an amendment to scrap the cap.

He said: “I was a little bit disappointed today by not necessarily some of the things that were within the King’s Speech, but some of those things that weren’t.”

The MP for Aberdeen South added: “This is a policy – an iniquitous, heinous policy – which was introduced by the former Conservative government in 2015.

“Each and every one of us in this chamber knows that it retains children in poverty – hundreds of thousands of children across these isles.

“In Scotland alone, it impacts 27,000 households. It’s estimated that 14,000 children would immediately be taken out of poverty were it to be scrapped, but it was not mentioned in the Government’s programme for government today.

“Instead, all we have heard is that a taskforce is going to be created – no timeframe for that taskforce, no indication of when that taskforce will conclude, and all the while, those children will remain in poverty.”

Plaid Cymru’s Westminster leader Liz Saville Roberts welcomed the taskforce but accused Labour of not prioritising children in poverty.

The Dwyfor Meirionnydd MP said: “The decision not to scrap the two-child benefit cap shows Labour choice not to prioritise the immediate needs in the here and now of nearly a third of children in Wales who live in poverty.

“Labour officials have repeatedly refused to make this so-called unfunded commitment, but the point is, and this matters: the decision not to fund it is a political decision.”

She said it is “interesting” that the taskforce was announced today, adding: “Is this the first indication of a U-turn on the part of Labour? If so, I would welcome it.”