The government’s welfare reforms, including benefit sanctions and the bedroom tax, are a central factor in the explosion in the numbers of impoverished people turning to charity food banks, an academic study has said.

The study, part of a three-year investigation into emergency food provision, was carried out by Hannah Lambie-Mumford, a Sheffield University researcher who co-authored a recently published government report into the extent of food aid in the UK.

That report concluded there was insufficient evidence to demonstrate a clear causal link between welfare reform and food bank demand in the UK. But Lambie-Mumford’s new study, to be published on Wednesday, says the rise in demand for charity food is a clear signal “of the inadequacy of both social security provision and the processes by which it is delivered”.

The report warns that as social security safety nets become weaker, there is a danger that charity food could become an integral part of the state welfare provision, or even an replacement for formerly state-funded emergency welfare schemes.

Lambie-Mumford’s study was based on 25 in-depth interviews with a range of food bank staff and volunteers in 2012 and 2013 and found many food banks were adapting to demand by scaling up food collection and storage provision “to accommodate the future trajectory of need”.

Her paper will be presented to an all-party committee of MPs which meets on Wednesday to finalise the terms of an inquiry into hunger and food poverty. The inquiry will examine the rise of food banks, an issue that has become politically charged as ministers attempt to deflect criticism that austerity policies, including welfare cuts, have had the effect of compelling more people on low incomes to rely on food aid.

Lambie-Mumford said her research showed that food banks were expanding to meet rising demand caused in part by a squeeze on welfare entitlements which made already poor people even worse off. This was compounded by inadequate processing of social security claims, including payment delays and “arbitrary and unfair” sanctioning decisions that left claimants without any income at all. There were other factors which had contributed to the rise of food banks, such as low wages and the rise in the cost of food. But it was important that MPs did not duck or underplay the importance of welfare reform. “The tricky thing is that welfare reform is the most political aspect of a political issue. But we should not shy away from it for this reason,” she said.

The welfare minister Lord Freud notoriously claimed last year that more people were going to food banks because the food was free, thereby triggering “almost infinite demand”. Last month Freud admitted people did not turn up “willingly” at food banks but said it was “very hard to know why” they did go.

The Trussell trust, which oversees a network of more than 400 food banks in the UK, has insisted repeatedly that welfare reform is the biggest driver of demand for food parcels. Its third-quarter data, published in March, showed that it helped 614,000 people in the first nine months of this year. Its final-year figures, expected next week, are likely to show that demand has more than doubled in the past 12 months. More than eight out of 10 food bank managers interviewed for the study acknowledged the impact of welfare changes and welfare processes as a factor in driving demand.

A DWP spokesperson said: “This report, which is based on just 25 interviews, fails to consider how welfare reforms are helping people off benefits and into jobs. The truth is that we now have record numbers of people in work, the highest employment rate for five years, and falling unemployment.” A DWP spokesman later added that the report “gave a one-sided view”.