The treasury minister David Gauke said last month that cash-in-hand payments to cleaners, plumbers and the like cost Britain £5bn a year in tax avoidance.

Christian Fraser went to Belgium to look at a novel way of bringing the informal economy out into the open.

Instead of handing over cash for domestic help, Belgians can convert cash into a book of service vouchers at the post office.

This system then allows domestic workers to have access healthcare, social protection and a pension.

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