Media playback is unsupported on your device Media caption Dame Louise Casey compares the government's Universal Credit welfare plan to "jumping over a cliff"

Families could be left homeless and destitute if Theresa May insists on pressing ahead with Universal Credit, a former top adviser has warned.

Dame Louise Casey urged the prime minister to delay the rollout of the new benefit system so it can be fixed.

A dozen Tory MPs are calling for it to be paused, the Daily Telegraph says.

Official figures show 24% of new Universal Credit claimants wait longer than six weeks to be paid in full - causing many to fall behind on rent.

That could make a big difference to families who were "close to the edge," Dame Louise told the BBC. They "will end up in dire circumstances, more dire than I think we have seen in this country for years".

The government says the new system, which merges six existing benefits into one, offers extra support and that budgeting and financial help is available.

Work and Pensions Secretary Mr Gauke is expected to make a decision in the coming days about whether the rollout should be accelerated.

'Work should pay'

But Dame Louise, who has advised four prime ministers on social policy over the past 18 years, including Mrs May, said the implementation had to be got right.

"I completely agree that we all should be wedded to the principle, and therefore the overall policy, that work should pay," she said.

But she added: "If it means that we are looking at more and more people that are ending up homeless, or ending up having their kids taken away, or ending up in more dire circumstances, that cannot be the intention.

"It can't be and it won't be the intention of Theresa May or [First Secretary of State] Damian Green or any of those people. I just don't believe that they would want that to happen."

She suggested ministers were blindly "pressing on" with the policy because they did not want to be accused of doing a U-turn. But she said: "It's like jumping over a cliff - once you have jumped, people end up at the bottom and we don't want that to happen."

Media playback is unsupported on your device Media caption Shadow work and pensions secretary Debbie Abrahams "commends" Tory rebellion against Universal Credit

Homeless 'because of Universal Credit'

Garry Dunningham, 24, lives in a tent by the river in Great Yarmouth.

He says he and his girlfriend were evicted from their shared flat about six months ago once their landlord found out they were on Universal Credit.

"Basically because we were on Universal Credit and he's had a lot of people not paying the rent... we got kicked out."

Garry says he has tried 58 private landlords across the town but no-one will take them.

"As soon as I go to meet them and say I am on Universal Credit, it's a no: 'We ain't got no rooms.'"

He says being homeless has affected his chances of finding work: "You need an address. It's a vicious circle."

He has even offered to pay rent and a deposit in advance "but they won't even do that".

"No-one's giving us the benefit of the doubt. You can't always judge everyone by what other people have done but that's what they're doing.

"I've walked down the street and there's been house after house empty... and no one will let us in."

Image caption Garry Dunningham, left, spoke to BBC social affairs correspondent, Michael Buchanan

The BBC understands Tory MPs, led by Heidi Allen, have written to Mr Gauke, demanding the national rollout of the policy be paused.

Shadow work and pensions secretary Debbie Abrahams welcomed the move, saying a "pause" could be used to bring in advance payments, rather than loans, for struggling families and to scrap charges for calling the Universal Credit helpline number, among other things.

Conservative MP Stephen McPartland said his concern with Universal Credit was that for "every pound these people earn, extra, the government's taking 63p back off them".

"To me that is an effective tax rate of 63%, which is ridiculous. So the lowest paid are effectively having to pay some of the highest taxes," he told BBC Radio 4's the World at One.

Media playback is unsupported on your device Media caption "The higher rate tax payers only pay 45p in the pound, so why are these low earners paying 63p?" asks Tory MP

The Department of Work and Pensions said Universal Credit was working and people were moving into work faster and staying in work longer than under the old system.

"The vast majority of claimants are paid in full and on time, and are comfortable managing their money. Advance payments and budgeting support is available for anyone who needs extra help," a spokesman said.

Dame Louise first came to prominence as Tony Blair's "anti-social behaviour tsar" and also led a programme for David Cameron to tackle "troubled families". She has now left the government to work for an international homelessness charity.

She also told the BBC she was concerned that a report she published last year on integration had been placed in a box marked "too difficult".

The government has yet to issue a formal response to the review, which accuses public bodies of ignoring or condoning divisive or harmful religious practices for fear of being called racist.