There has been a dramatic increase in demand for food banks and charitable help in the UK, with more than 20m meals provided in 2013 – a 54% increase on the previous year.

A joint report Monday from Oxfam, Church Action on Poverty and the largest operator of food banks, the Trussell Trust, says that much of the increased demand is coming from poor people in affluent areas including Cheltenham, Welwyn Garden City and the northern part of the Lake District, where some food banks report user numbers doubling or even trebling. The Trussell Trust said it was helping to feed 300,000 children, a situation it described as a national disgrace. The report's authors said the poor were caught in a perfect storm of food prices soaring 43.5 % in the past eight years, while over the same period the disposable annual income of the poorest 20% fell by an average of £936.

Low and stagnant wages, zero-hours contracts, benefit sanctions and energy costs are among the factors driving people into food poverty.

Food bank users cited in the report included a woman who raided her daughter's jar of saved pennies to buy her milk; a woman who keeps hunger at bay on hot lemon, water and sugar; and a woman with a baby daughter who is left with £6 from benefits in school holidays, because her teaching assistant partner is paid only in term time.

A government spokesman said: "It's simply not possible to draw conclusions from these unverified figures from disparate sources."

However the charities are calling on the government to take urgent action to collect that evidence, to understand the scale and cause of the increase in food bank usage.

Chris Mould, chair of the Trussell Trust, called the 300,000 children they are helping a national disgrace. "The troubling reality is that there are also thousands more people struggling with food poverty who have no access to food aid, or are too ashamed to seek help, as well as a large number of people who are only just coping by eating less and buying cheap food.

Mark Goldring, chief executive of Oxfam, said the fact that food banks were needed in the 21st century was a a stain on the national conscience. "We truly are living through a tale of two Britains; while those at the top of the tree may be benefiting from the green shoots of economic recovery, life on the ground for the poorest is getting tougher."

The spokesman for the Department of Work and Pensions said there was still a strong welfare system safety net, overlooked in the report.

"We've also helped families by cutting the cost of living, more people are in work helping to support their family, benefits are being paid to claimants more quickly and according to independent experts fewer people report struggling with their food bills compared with a few years ago."

In the report – which will feature in a Channel 4 Dispatches documentary, Breadline Kids, on Monday night – the charities estimate that the three main food aid providers, Trussell, Fareshare and Food Cycle, gave out over 20m meals in 2013-14, up from 13m a year earlier. The Trussell figures are the most robust, and show that between April 2013 and March 2014 the trust gave three days' worth of emergency food supplies to 913,138 people, the equivalent of more than 8m meals.