THE Archbishop of York, Dr Sentamu, is being urged by charities and trade unions to endorse the idea of making the Living Wage compulsory.

Dr Sentamu chairs the Living Wage Commission, which was established last year to examine the impact of the wage since it was introduced in 2001, and the future of the scheme.

In an open letter before the Commission's final meeting last week, the charity War on Want and the general secretaries of nine trade unions asked Dr Sentamu to ensure that the Commission recommends that the Living Wage becomes mandatory. It is currently set at £7.65, or £8.80 for those living in London.

The letter says: "While we pay tribute to all those local and voluntary campaigns that have forced the issue of low pay on to the political agenda over the past 12 years, the worsening of the problem today proves that it is simply not possible to rely on voluntary initiatives alone.

"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.

"Equally, in the globalised economy of the 21st century, we would like the commission to call for a requirement on UK employers to guarantee a Living Wage throughout their global supply chains."

The signatories expressed strong support for the commission's preliminary report, Working for Poverty, which was released earlier this year. But they also wrote that they would be "disappointed" if the final report, due in June, calls only for a continuation of the existing voluntary Living Wage scheme.

A motion was passed at the General Synod in November 2012, encouraging the Church of England institutions to pay their employees the Living Wage, and affirming the "Christian values" that, it said informed the concept.

All Methodist churches and organisations are obliged to pay the Living Wage, after a decision by the Methodist Conference in 2010. A 2008 motion at the United Reformed Church's General Assembly called on all URC congregations to support paying the Living Wage. The Church of Scotland and the Baptist Union have also expressed support for the scheme.

Last week, the Office of National Statistics released new figures that suggest that as many as 1.4 million workers are on so-called "zero-hours contracts", which do not guarantee a minimum number of hours of work each week.

Recent research by the Trades Union Congress has also found that 57 per cent of those on zero-hours contracts were paid less than the Living Wage.