Ministers have been accused of making “reckless” staffing cuts after it emerged the department responsible for welfare benefits has lost 21 per cent of its workforce since the controversial universal credit system was introduced.

Campaigners warned staff in the Department for Work and Pensions (DWP) were under “intense pressure” to deal with growing workloads after government accounts data revealed the workforce had been reduced by 19,189 since 2013, amounting to a loss of one in five employees.

Universal credit claimants meanwhile said they had been left struggling to put food on the table after being denied financial support they were eligible or ordered to pay back large sums of money due to overpayments made as a result of errors by caseworkers.

It comes after the UK’s spending watchdog revealed fraud and error in the welfare bill were at their highest levels since 2006, with benefit claimants and pensioners losing out on £2bn that they were entitled last year to because officials short-changed them.

Another £1.1bn was overpaid to claimants due to errors by caseworkers, or because the recipient failed to give the right details about their income – through the complex online portal system – on time.

In one case, a couple in Scotland said they were forced to “clean out their savings just to survive” after the DWP made two errors on their benefit calculations in the space of eight months.

Gordon Dunlop, 44, said he and his wife Samantha, 36, both mature students living near Dundee with their two teenage children, had applied for universal credit last September. After submitting all the relevant documents, they were placed on a high award.

But in March, when Mr Dunlop made a minor amendment to their claim due to a small rent increase, he was informed by a caseworker that they had been overpaid, and must repay £7,000 – meaning they received no support over the following months.

In May, Ms Dunlop stopped receiving her student loan, but although the couple informed the DWP of this, their entitlement did not change and they continued to receive no universal credit.

Two months later, the couple were informed they had been underpaid more than £1,000 because the caseworker had made “several errors”.

Mr Dunlop told The Independent: “We had been struggling. We had to use all our savings to try and survive, because we were getting no help from them, and it basically cleaned out all our savings because we had to survive on something. We had to live off food we had stored in the freezer.

“It was just chaos. And it’s extremely stressful. The bills keep rolling in. We worried about how we were going to survive from day to day. And now we’re always fearful that it will happen again.”

The Public and Commercial Services Union (PCS), which represents people working for the government, said the staffing cuts in the DWP had been “hugely detrimental” to the ability of its members to serve the public effectively.

Mark Serwotka, general secretary of the PCS, said: “Our members in social security are trying hard in difficult conditions to help universal credit claimants, benefit claimants and the disabled. What they need is a properly resourced department, not cuts and increased workloads.”

Margaret Greenwood, shadow work and pensions secretary, said it was “both reckless and irresponsible” of the DWP to cut staffing by a fifth at the same time as rolling out the “deeply flawed” universal credit programme, and that staff and claimants were suffering as a result.

The Liberal Democrats’ DWP spokesperson, Christine Jardine, echoed the remarks, saying it was “astonishing” to see the department cut its workforce to such an extent when “so many people are suffering from DWP’s blunders”.

Abby Jitendra, policy and research manager at the food bank provider the Trussell Trust, said: “It’s really important that a big change to that system, like universal credit, is done right. Making sure there are enough frontline staff to give people a personalised service is crucial.

“Universal credit should be protecting people from needing a food bank – but we need to make sure it’s properly resourced if it’s to do so.”

It comes after it emerged in March that work coaches – the frontline staff in jobcentres – are going to be handed bigger workloads to reduce costs, with their caseload set to rise from around 130 to more than 280 by 2024-25.

Meanwhile, ministers were recently accused of “wasting huge chunks of desperately needed resources” after a £200,000 newspaper advertorial vowing to “set the record straight” on universal credit was published on the same day charities revealed claimants were “selling sex to survive”.