Social bond schemes, in which private investors give money to projects to tackle social deprivation and are paid if they are successful, are being piloted in four local authorities.

Sir Ronald Cohen, co-founder of Social Finance which helped develop the bonds, say the schemes will be "extremely powerful" and will "revolutionise" the way charities and non-profit organisations tackle deprivation.

But Guardian columnist Polly Toynbee said social bonds were "a kind of PFI", are "incredibly complicated", would "drain off money" to accountants, and "the government will have to pay out whatever the results".

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