As the final meeting of the Archbishop of York's Living Wage Commission approaches, several groups have called for the Living Wage be made compulsory.

A letter signed by the charity War on Want and a number of trade unions sent to Archbishop John Sentamu said: "We are concerned that the final report of the Living Wage Commission must reflect the urgency of the low pay scandal.

"We believe that the time has come for the living wage to be more than just an optional extra over and above the national minimum wage, and we believe that the living wage commission must also make that call."

The Living Wage Commission, an independent year long investigation into low pay, was set up in 2013 by the left of centre thinktank Compass.

At its inception, Archbishop Sentamu was quoted in the Guardian as describing the low pay situation in the UK as a "national scandal". He accused the political classes of offering only "warm words" and "sticking plasters" to the problem.

This is the most recent push in a campaign on the issue that has been ongoing for over a decade. War on Want has said that the initial strategy of encouraging a non-compulsory living wage among companies is insufficient to deal with the problem of low wages.

Sources within the Living Wage Commission are reported to have expressed the view that up until now there has been relatively little outside pressure for the commission to move towards recommending a compulsory living wage.

John Hilary, director of War on Want, told Christian Today: "We are concerned that the urgency of the situation hasn't been recognised in terms of what people are calling for.

"While calling for a voluntary living wage over and above the minimum wage might have been a good idea 12 years ago, it's clear we're now in a different space.

"Politically, it is absolutely crucial that we use the widespread support for the principle of a living wage in order to take it further."

These calls come as research published this week by the Resolution Foundation thinktank reveals that almost three in 10 people on zero hours contracts are not working as many hours as they would like.

New figures released today by the Office for National Statistics confirm that there are 1.4 million UK employees on zero hours contracts, a substantial revision from previous estimates of 580,000.

A study by the Trade Union Congress has also revealed that 57 per cent of zero hours contract employees are on minimum wage.

Joint research by the Living Wage Foundation and Nationwide found that just 9 per cent of people believed they could live sustainably on the current minimum wage of £6.31 per hour.

The research also found that the difference between the living and minimum wage, £148.07 per month, would most likely be used by those on the minimum wage to provide basic essentials for their families.

Currently, the Living Wage Foundation accredits 630 employers from across the UK with paying a reasonable living wage of £7.65 per hour in most of the country, and £8.80 in London.

Last week, Ed Miliband was quoted by the BBC saying that in his view the number of zero hours contracts had reached "epidemic" levels.

A spokesman for the Living Wage Commission told the Guardian that it had been hearing views from businesses, trade unions and low-paid workers, and planned to deliver its finding on 24 June.