David Cameron has been blamed by 27 Anglican bishops for creating a "national crisis" which has seen 500,000 people visit food banks since Easter last year.

In one of the most significant political interventions by leading members of the Church of England since the Faith in the City report in 1985, 25 of its bishops have blamed "cutbacks to and failures in the benefit system" for forcing people to use food banks. They are joined by two bishops from the Church in Wales, 14 Methodist districts chairs and two Quakers.

In an open letter published in the Daily Mirror on Thursday, the faith leaders write: "We must, as a society, face up to the fact that over half of people using food banks have been put in that situation by cutbacks to and failures in the benefit system, whether it be payment delays or punitive sanctions."

The intervention, part of the End Hunger Fast campaign which will be launched at the start of Lent on Ash Wednesday on 5 March, follows the description of the government's welfare reforms as a disgrace by the head of the Roman Catholic Church in England and Wales, Vincent Nichols.

The Anglican bishops express astonishment that people can be going hungry in the world's seventh richest country. They say that 500,000 people have visited food banks since Easter last year, 5,500 have been admitted to hospital with malnutrition and 20% of mothers are "skipping meals to better feed their children".

The bishops write: "We often hear talk of hard choices. Surely few can be harder than that faced by the tens of thousands of older people who must 'heat or eat' each winter, harder than those faced by families whose wages have stayed flat while food prices have gone up 30% in just five years. Yet beyond even this we must, as a society, face up to the fact that over half of people using food banks have been put in that situation by cutbacks to and failures in the benefit system, whether it be payment delays or punitive sanctions."

The bishops note that Lent will mark the beginning of the Christian tradition of fasting at a time when half a million people are going hungry. They write: "We urge those of all faith and none, people of good conscience, to join with us. There is an acute moral imperative to act. Hundreds of thousands of people are doing so already, as they set up and support food banks across the UK. But this is a national crisis, and one we must rise to. We call on government to do its part: acting to investigate food markets that are failing, to make sure that work pays, and to ensure that the welfare system provides a robust last line of defence against hunger."

Rachel Reeves, the shadow work and pensions secretary, said: "This letter should be a wake-up call to David Cameron. His government's policies are making life harder for families with a cost-of-living crisis making workers £1600 worse off and the bedroom tax forcing hundreds of thousands to food banks. This Tory-led government's welfare reforms have penalised, rather than helped, those doing the right thing."

The letter will be seen as a significant political intervention because the bishops directly blame the government's cuts for welfare cuts. Unlike the Faith in the City report, which was launched by the late Archbishop of Canterbury Robert Runcie, the letter is not a formal Church of England initiative.