Tory MPs have blocked an attempt to obtain a government analysis of the impact of Universal Credit on people’s incomes.

MPs voted 299 to 279 against an attempt by Labour that to secure the release of the assessment drawn up by officials – a majority of 20.

The move followed reports that Work and Pensions Secretary Esther McVey warned the Cabinet some claimants could be £200 a month worse off under the new benefit system.

Last week she admitted during an interview that “some people will be worse-off” on UC than under the previous system.

Shadow work and pensions secretary Margaret Greenwood told the Commons today UC had been “beset with flaws in its design and delivery” and was “causing immense hardship”.

She said that 3.2 million families with children could lose around £50 a week, adding: “People are worried, but there’s no clarity from Government.”

But McVey insisted the government had taken a “mature approach” to the rollout of the system.

McVey insisted the rollout of Universal Credit would continue, but said she would ensure the Government “get it right”.

“We will make sure we get this benefit right. You know for why? Because the genuine concerns of the people on our backbenches want to get it right,” she told MPs.

It came as the government revealed it is facing a benefits bill of more than £1.5bn after underpaying tens of thousands of disabled claimants.

An estimated 180,000 people are due arrears payments totalling £970m after under-receiving Employment and Support Allowance (ESA), Department for Work and Pensions (DWP) papers have shown.

And the cost of paying them extra after their claims have been corrected is estimated to add another £700 million over the next seven years, taking the total additional bill to £1.67 billion, an internal analysis released on Wednesday shows.