A summer of discontent “lies ahead” and a million more children risk being plunged into poverty unless Theresa May rolls back “cruel and vindictive” universal credit plans, former Prime Minister Gordon Brown will warn.

Brown, who will later call for the Government to do a U-turn on the highly-criticised benefit payments scheme to be rolled out fully next year, will say the system will increase reliance on food banks.

He will warn that the plans could trigger “poll tax-style chaos” reminiscent of national protests against the Margaret Thatcher-imposed system in 1990, which contributed to her ousting later that year.

In Edinburgh, Brown is expected to say: “Surely the greatest burning injustice of all is children having to go to school ill-clad and hungry. It is the poverty of the innocent – of children too young to know they are not to blame.

“But the Conservative government lit the torch of this burning injustice and they continue to fan the flames with their £3billion of cuts. A return to poll tax-style chaos in a summer of discontent lies ahead.”

His comments follow reports that work and pensions secretary Esther McVey has been privately warning that millions of families could lose out on £200 a month as a result of the rollout.

She reportedly said that half of all lone parents and two-thirds of working -age couples with children could lose  around £2,400 a year.

It emerged over the weekend that ministers have been growing increasingly worried abut the potential effects of the system, which sees separate benefit payments rolled into one.

Charities have criticised scheme – created by former work and pensions secretary Iain Duncan-Smith – as badly-designed after many claimants have faced delays and rent arrears.

The scheme was created to simplify the welfare system but claimants have complained of difficulties in the application process.

Last week, McVey unveiled plans for a £39 million partnership with charity Citizens Advice to support applicants in getting their first payments on time.

Brown will say: “Esther McVey would not be announcing last week millions for Citizens Advice to aid the rollout of universal credit unless they were not deeply worried about the chaos ahead.

“And it is the fear of a poverty crisis that had led Michael Gove to announce funding for food banks.”

Gove, secretary for Environment, Food and Rural Affairs, last week announced a £15 million subsidy to support food redistribution to thousands of UK charities.

Some 250 million meals – or 100,000 of food surplus – will be given out homeless shelters, lunch clubs and food banks.

Brown will add: “As one of the architects of tax credits I remind people that it was difficult enough to introduce them even when we were spending billions more raising benefits.

“But to impose universal credit – and to force three million to reapply for their benefits next year – when, on top of a child benefits freeze, the government is spending £3 billion less, is chaotic, cruel and vindictive, far beyond austerity.”

In the speech, the former chancellor will use his hometown of Kirkcaldy in Fife as an example of the failures of universal credit, saying that food bank use has doubled in one year.

“For the first time that any of us can remember, the safety net is not now the welfare state but charity – and the lifeline for families in need is not social security but food banks. Voluntary groups are now being swamped with desperate and almost unanswerable requests for help.”

He will add: “[Universal credit] was advertised as making work pay and empowering those on low incomes but in fact two-thirds of poor children are now in family where someone is working.”

The Labour ex-chancellor increased tax credits between 1997 and 2007 in a bid to lower child poverty, and will warn that four million children now live below the poverty line and the figure will increase by another million by 2022.