Hidden charges and other practices are adding to the bills of millions across the UK, the party will say.

Analysis in a Labour report will also warn that the poor are often having to pay more than the well off.

Earlier this year Labour floated the possibility of bulk buying electricity to sell on to the public at a discount.

It pointed to the experience in Belgium where the Labour party has helped to cut the energy bills for thousands of households through a similar scheme.

"This report will highlight the extent of rip-off practices," a Labour source said.

The party also wants to make markets work more effectively for customer and businesses.