Fresh controversy has flared over the Government's flagship Universal Credit benefits system after a report said claimants are routinely "in the dark" about how much they should receive.

The Child Poverty Action Group (CPAG) said claimants also did not know how their awards were calculated or how they could challenge decisions.

The group accused the Department for Work and Pensions (DWP) of having "inadequate" communications and of making administrative errors likely to result in claimants getting the wrong amount.

Meanwhile, a separate report from a parliamentary committee said the DWP must "prove it is up to the job" before a single existing benefit claimant is moved onto Universal Credit (UC) by a process known as "managed migration".

The House of Commons Work and Pensions Committee said Amber Rudd's department should immediately set up "tests of operational readiness" based on recommendations from a number of experts and should ensure it can meet those tests before beginning pilots of the migration.

Committee chair Frank Field said: "Six months after we started pressing them on the next potential UC disaster on the horizon, the department is yet to prove it's up to the job of so-called 'managed migration'.

"Anyone who sees their income slashed or their circumstances and life chances reduced, or any of the other messes UC is getting people across this land into, will find no comfort in learning it didn't happen on purpose.

"Does DWP want to explain to them it didn't bother to find out how they might be affected? Will it be a comfort to learn DWP did take a look at that, but didn't bother to apply its findings? DWP should not move one person onto UC until it does test, and does learn, and proves it is ready to safely do so."

Universal Credit (UC) rolls six different benefits into one, so claimants often cannot tell what the different components are, said the CPAG.

Spotting errors can be difficult or impossible because online monthly payment statements only give basic information, it was claimed.

The group cited a number of cases including a working mother with two part-time jobs who was £400 a month worse off because of errors, and a grandmother wrongly subjected to the bedroom tax and a non-dependant deduction, leaving her underpaid for months.

Alison Garnham, chief executive of the CPAG, said: "Transparency should be at the heart of a fair social security system, but our research shows Universal Credit claimants do not always understand the amounts they're getting, so it's harder for them to pick up on mistakes or to predict how their awards might change.

"That is all the more worrying as the number of Universal Credit claims is set to double this year to three million and the scope for misunderstandings, omissions and errors is vast.

"Because UC is an all-in-one benefit, with all your eggs in one basket, when things go wrong for claimants the financial fallout can be dire, but there are practical, inexpensive changes the DWP can make to clear the fog.

"The department must improve the information it provides so that Universal Credit claimants are not floundering in the dark about their award. Clear and accessible information on how decisions are made and your right to appeal is the bare minimum we should expect from a modern benefit."

A DWP spokesman said: "More than 1.8 million claimants receive a monthly statement advising them of their entitlement, how it has been calculated and what to do if they think the payment is incorrect.

"Help is also available from work coaches, the freephone Universal Credit helpline, and through our 'Help to Claim' partnership with Citizens Advice."

The DWP said later: "The Work and Pensions Select Committee welcomed our pilot approach to moving people to Universal Credit from the old benefit system.

"We are taking a slow and measured approach, and will return to Parliament before increasing the number of people moving onto the benefit.

"We have a proven track record of delivering major programmes of change as safely as possible.

"In the last year we have successfully moved 250,000 people from Universal Credit live service to full service. More than 1.8 million households are now supported by Universal Credit."

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