Criticism of the Government's flagship welfare push to bring-in Universal Credit has been rejected by Work and Pensions Secretary Stephen Crabb.

The minister dismissed claims in a new report by the Resolution Foundation that the major reform has "serious" design flaws which must be resolved before rolling it out across the country.

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The think-tank, headed by former Tory Minister David Willetts, warned that Universal Credit had been taken too far away from its original purpose because of changes driven by planned savings in the welfare budget.

The report urged Mr Crabb to "reclaim" the benefit from the Treasury after Iain Duncan Smith quit the work and pensions post partially in protest that the aims of Universal Credit were being eroded.

Mr Crabb insisted that motivating jobseekers via Universal Credit changes was working.

"Frankly, under the old system you were just dumped on benefits, you got your cash payments week in, week out.

"Our vision of the welfare system is we want to see people moving through it and emerging on the other side fully economically independent. So we have these teams of work coaches who provide that practical support," Mr Crabb told the BBC Radio 4 Today programme.

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The Cabinet minister said reforms like abolishing the "crazy" rule limiting people on benefits to 16 hours work a week were producing positive results.

Mr Crabb, who said he was still in talks with the Treasury about how the planned £12 billion cut in the welfare bill would be achieved, insisted that Universal Credit would be successful across the country.

"We have had half a million people who have now made a claim through Universal Credit, we now have 250,000 people currently receiving Universal Credit, and when you compare those groups of people with a similar group of people receiving the old Jobseeker's Allowance, you'll see that those people who are on Universal Credit are more likely to be spending more hours looking for work, they are more likely to be finding work and, when they find work, they are more likely to be earning more and looking to increase their hours, so Universal Credit is already working," Mr Crabb said.

Universal Credit, being put into place across the country, replaces income-based Jobseeker's Allowance, income-related employment and support allowance, income support, child tax credit, working tax credit and housing benefit.

The Resolution Foundation said it risked being reduced to little more than a complicated vehicle for cutting the benefits bill.

David Finch, senior economic analyst at the foundation, said: "As Universal Credit begins the roll-out of its full service this month, now is the right time for the new Work and Pensions Secretary to take stock of progress to date.

"It is a reform with lots of potential, but it has veered off track over recent years, particularly following a series of sharp cuts in support to working families.

"With UC's main goal of making work pay now under serious threat, the Secretary of State should reclaim the project from the Treasury.

"He should prioritise support on those most likely to respond, such as single parents and second earners, ensure UC does more to help those already in work to progress, and iron out some of the practical concerns that have arisen during the initial pilots."

The Government announced that UC was now in every jobcentre across the country for single jobseekers.

More than 45,000 people have made a claim so far, with in excess of 9,500 new claims made every week.

Shadow work and pensions secretary Owen Smith said: "This announcement shows Stephen Crabb thinks working families should put up the bunting to celebrate the rollout of Universal Credit cuts that will see 2.5 million an average of over £2,100 a year worse off.

"Only a Tory Government with as warped a sense of priorities as this one could issue a statement lauding the rollout on the same day an independent expert report from the Resolution Foundation shows Tory cuts will completely undermine work incentives in the programme.

"The Tories should stop slapping themselves on the back for delivering cuts to working families right across the country and instead listen to Labour's calls for an urgent U-turn."