The National Council for Voluntary Organisations is urging charities to join the campaign for a global ‘Robin Hood' tax on banking transactions that could raise billions of pounds for good causes.
The organisations say the tax could raise up to £250bn a year globally, half of which would be split equally between projects to reduce poverty and tackle climate change.
The other half would be kept by the countries that levied the tax.
Campaigners say the Government could use the revenue to avoid cuts to public services and to meet its target to halve child poverty.
Stuart Etherington, chief executive of the NCVO: "We believe in the good society, which promotes fairness and social justice. This tax would help to achieve our aim by using a tiny proportion of monies transferred between banks every day to pay for crucial aid and support for those who need it."