The poorest households spend 40% of their income on housing, food and fuel, a huge increase on a decade ago, according to research uncovered by an all-party parliamentary inquiry into hunger and food poverty.

The evidence suggests that while the cost of living crisis has hurt every socio-economic group, it has been a disaster for the poorest households. The proportion of income that the poorest households spend on necessities rose by nine percentage points between 2003 and 2012, in the biggest rise endured by any economic group.

According to a cross-party inquiry led by Labour MP Frank Field, the disproportionately large increase seen in the poorest households is due entirely to rising housing and fuel costs – the proportion of income spent on food is the same as a decade ago.

UK households combined spent £34.3bn on energy in 2013, a real-terms increase of 131.1% on the £14.8bn spent in 2003. Had energy prices risen in line with the RPI over the same period, households would have spent £20.6bn on energy in 2013 – an increase of just 39.2% on 2003. It is claimed that cuts have duly had to be made by the poorest households in the quantity or quality, or both, of food purchases. According to an evidence paper due to be published by the inquiry this week, these trends may help explain why so many households now rely on food assistance. Last month religious leaders and faith groups called on the government to take action to tackle what they described as a "national crisis" of rising hunger and food poverty, as figures suggested that more than a million Britons have been helped by food banks in the past year.

More than 40 Anglican bishops and 600 church leaders signed a letter calling on David Cameron, Nick Clegg and Ed Miliband to tackle the causes of food poverty, including low wages, rising food prices and an inadequate welfare benefit safety net.

The cross-party inquiry – co-chaired by Field, a former welfare minister, and the bishop of Truro, Tim Thornton – is investigating the reasons behind the growth of food banks and alternative sources of emergency food. "These figures show that the government has totally misjudged the politics of this issue," he said.

"All parties are in the dock, as the figures show that while the crippling pincer movement on poor people's incomes began long before the coalition was elected, it nevertheless has continued with the sanctions policy often being unjustly applied.

"I hope the publication will start a serious discussion in all political parties based around the evidence that something quite fundamental has been squeezing the incomes of the very poorest."

Extracts from evidence submitted to the inquiry was also made available to the Observer. A Trussell Trust food bank organiser in Greenwich, south London, told the inquiry: "The working low-income group have seen their wages remain static … while the cost of living, particularly fuel, has risen. Something has to give and the only optional item in their budget is the spend on food."