A cross-party group of MPs has called for the next phase of universal credit to be put on hold until ministers can show that disabled claimants will be properly protected from the potentially disastrous consequences of moving to the new system.

The Commons work and pensions committee says there are insufficient safeguards for claimants who will be worse off financially when approximately a million disabled people on employment and support allowance (ESA) move on to universal credit over three years from 2020.

This would potentially leave some of the social security system’s most vulnerable claimants isolated, destitute and in some cases relying on their dependent children for care, the committee says in a report.

It says the government should not seek parliamentary approval for regulations covering the “managed migration” of about 3 million claimants on ESA and working tax credits to the new system, but should wait until lessons can be learned from a pilot scheme starting next year covering 10,000 claimants.

The report highlights the removal from universal credit of disability premiums that are worth up to £64 a week for a single person. The premiums are designed to meet the extra costs of living alone without a carer. Approximately 500,000 people in the UK receive the severe disability premium, enhanced disability premium or both.

Earlier this year the government announced it would provide transitional protection for recipients of the premiums after a court case brought on behalf of two disabled men revealed they were unable to afford basic needs after they moved on to universal credit and found themselves £178 a month worse off.

The committee says the government made a “serious error” in removing disability premiums from universal credit in the first place. While it had since introduced protections, these could still be lost if claimant circumstances change, and will not apply to new claimants.

“Removing vital additional support offered by the disability premiums from universal credit risks disabled people living more isolated lives, relying on unpaid care (including from their own dependent children) or simply being unable to complete certain basic daily tasks,” the report says.

It calls on the government to consider introducing a new “self care” payment into universal credit for all claimants who would have received the disability premiums.

Although the Department for Work and Pensions (DWP) has pledged that “severely disabled” claimants will be better off under the new system, the committee says this will come at the expense of those claimants judged to be “less severely disabled”.

The committee also says that currently 100,000 families with disabled children will be worse off. It says officials have no clear idea what the impact will be on families facing a financial shortfall, or the knock on effects on local care services.

Frank Field MP, the chair of the committee, said: “The government’s plans will see ‘very’ disabled people getting the extra help they need at the cost of other disabled people. We have already seen the terrible cost of the department’s failure to find out what is happening to the most vulnerable claimants in the transition to universal credit.

“People receiving the disability premiums are already, by definition, managing in some of the most difficult circumstances imaginable in our society, and this includes disabled children, and children forced to care for a disabled parent. It would be a terrible betrayal of these people to allow another failure of planning in this mega reform to worsen their situations, even one bit.”

The report echoes fears of campaigners who have warned that the managed migration to universal credit could see disabled and ill people falling though the net. That warning was repeated by the government’s own advisers, the social security advisory committee, in October, which led to ministers last month promising to make changes.

A DWP spokesperson said: “More than a million disabled people will be better off by £100 a month under universal credit and £3bn of funding will help protect families as they move over from the old system.

“Universal credit does work for the vast majority, and the managed migration regulations are set to be debated in parliament in due course.”