“My children both have a cooked meal at lunch because they have free school meals. My cupboard’s full of tins,” Kayleigh tells me from her two-bedroom house in Lancashire. The 30-year-old single mother is in a position no parent ever wants to face – working out how she will feed her young son and daughter for the next six weeks.

Kayleigh used to have a good job as a stock taker for a large insurance company, but since having her children she has looked after them full-time: Lewis is eight and Olivia is five. For years, the three have got by with income support, housing benefit and child tax credits, but as of 19 November, Kayleigh was told to apply for universal credit: the system now rolling out nationwide that combines multiple benefits.

A “built-in” delay in universal credit means claimants such as Kayleigh are forced to wait at least 42 days before receiving their first payment. That’s six weeks without benefits. Kayleigh has to wait until 1 January for her first payment of universal credit. In the meantime, she has £34 a week of child benefit to live on.

“I’m struggling to heat the house and when we go to the shops, I have to say no,” she tells me. “Then the children wonder why Mum has not got money.”

It’s a small mercy that child benefit isn’t affected by the shift to universal credit. If it were, Kayleigh would now have no income at all. She is allowed one small advance of universal credit – around 50% of a monthly payment that she’ll have to pay back – but is doing her best to hold off claiming it for a week or two.

“I’m leaving it so we can have a Christmas,” she says. “I want to be able to buy my children the odd present.”

The Equality Trust has warned that universal credit’s built-in delay could push millions into debt. The thinktank found a staggering 7.5m households don’t have enough savings to cover six weeks’ worth of bills. That means jobseekers, disabled people and low-wage workers, among all those in the process of being transferred to universal credit, could now face getting through the Christmas period with payday lenders, food banks and rent arrears.

Once on universal credit, the odds are stacked against families to find their way free of debt. Last week, the chancellor proudly stated the “taper rate” on universal credit (how quickly the benefit is withdrawn according to a claimant’s earnings) will drop from 65% to 63% – effectively meaning the low waged can hold on to more of what they earn. But what he didn’t say was that if a single parent such as Kayleigh worked 150 hours a month, that would be worth just an extra £26. To put that in the bigger picture, Kayleigh could find a job tomorrow, and after taxes and the withdrawal of universal credit, she would keep barely a third of her wages. Compare that to someone in the richest 1%, who according to the Equality Trust’s calculations, keeps 53% of their additional earnings.

As it is, Kayleigh has no choice. Because her daughter has now turned five, benefit rules mean she has to look for at least part-time work. If she doesn’t, she’ll have her universal credit sanctioned by up to £10.40 a day for three months. Benefit sanctions can, potentially, stretch to three years.

For the last fortnight, she has completed the compulsory 35 hours of job searching each week: wading through anything she is qualified for that might fit the hours she needs. There aren’t many jobs available when you’ve been out of work for nine years and there’s no one to look after the children after 3pm. “I’m running out of options,” she says. “I’m sending my CV to all the main supermarkets just on the off-chance they may have something in the future.”

That’s what it is to be a so-called “benefit claimant” now: the government is free to withhold your money, but if you don’t keep up your end of the bargain, they’ll still punish you for it.

Kayleigh is currently relying on a cold weather payment to cover her gas and electric, and her mother is buying the family bits of food: milk, bread, pasta, rice and some chicken nuggets as a treat for the kids. “But she’s disabled so hasn’t got much money herself,” Kayleigh says. Kayleigh’s grandma helps too. Liam is lactose-intolerant and his nan uses part of her pension to buy him milk and butter that won’t make him ill.

As another insight into the workings of universal credit, as Kayleigh waits for her money to come in, she doesn’t even know how much is due: when she put in her claim, the system “forgot” to add her children and didn’t calculate it properly.

“It’s hard, but we’re in the same boat as most people,” she says. She counts herself lucky that she and her children are having Christmas dinner with her mum.