Massive cuts to social safety nets have led to "destitution, hardship and hunger on a large scale" in Britain, with more than half a million people now forced to rely on food banks for sustenance, key poverty charities have warned in a report.

Welfare changes and mistakes by Jobcentre Plus staff are causing delays in benefits and errors or sanctions, which push vulnerable people into precarious situations, the report from Church Action on Poverty and Oxfam warns. The charities want an urgent parliamentary inquiry.

"The shocking reality is that hundreds of thousands of people in the UK are turning to food aid," said Mark Goldring, Oxfam's chief executive. "Cuts to social safety nets have gone too far, leading to destitution, hardship and hunger on a large scale. It is unacceptable that this is happening in the seventh wealthiest nation on the planet."

The report, Walking the Breadline, is backed by the Trussell Trust, the UK's biggest provider of food banks. It blames the increasing pressure on food banks on far-reaching changes to the benefits system, as well as on unemployment, increased underemployment, low and falling incomes and rising food and fuel prices.

Changes to the benefit system are the most common reasons for people using food banks, including delays in payments, sanctions, sickness benefit reassessments and changes to crisis loan eligibility rules, according to the report.

It outlines the case of Kay, a single parent in her 30s who was required by her Jobcentre Plus adviser to search for six jobs each fortnight. When the job club she attended lost internet connectivity one week, she only managed to inquire about one vacancy, looking at five more the following week.

At her next visit to the Jobcentre, her adviser said her search was "not good enough" because her six job searches were not spread evenly. She was sanctioned a week's money of £71 and forced to rely on her family for financial support.

The energy secretary, Ed Davey, told MPs this month it was "completely wrong to suggest there is some sort of statistical link between the benefit reforms we're making and the provision of food banks".

But the report concludes: "There is clear evidence that the benefit sanctions regime has gone too far and is leading to destitution, hardship and hunger on a large scale. There is a real risk that the benefit cuts and the introduction of universal credit … will lead to even larger numbers being forced to turn to food banks. Food banks may not have the capacity to cope with the increased level of demand."

The Guardian reported this week that many food banks were struggling to meet the explosion in demand for food parcels.

The report says that keeping the national minimum wage and benefit levels in line with inflation will allow families "to live with dignity and … afford to feed and clothe themselves and stay warm".

Niall Cooper, chief executive of Church Action on Poverty and the report's lead author, said: "The safety net that was there to protect people is being eroded to such an extent that we are seeing a rise in hunger. Food banks are not designed to, and should not, replace the normal safety net provided by the state in the form of welfare support."

The report calls for the Commons work and pensions select committee to conduct an urgent inquiry into the relationship between benefit delay, error or sanctions, welfare reform changes and the growth of food poverty.

It also urges the Department for Work and Pensions to publish data on the number of people sanctioned, and on referrals from Jobcentre staff to local food banks.

Imran Hussain, head of policy for Child Poverty Action Group, said: "It's a national scandal that half a million British people are now having to turn to food aid. It's a problem that has quickly escalated and shows that something has gone badly wrong with the safety net that is supposed to help families in need.

"It is particularly concerning that more and more of the families seeking food aid are actually in work but on poverty pay and facing cuts to their tax credits."

Mary Creagh, Labour's shadow environment secretary, called the figures "shocking" and urged the government to change tack.

"The UK is the seventh richest country in the world, yet we face a growing epidemic of hidden hunger, with people increasingly unable to meet their family's basic needs," she said.

A DWP spokeswoman said the majority of benefits were processed on time every day. She said: "We welcome the contribution voluntary organisations and food banks, including the Trussell Trust, play in supporting local communities, beyond the safety net provided by government.

"That is why Jobcentre Plus – for the first time – is now referring people to their services. Our welfare reforms will improve the lives of some of the poorest families in our communities, with the universal credit simplifying the complex myriad of benefits and making three million households better off."