Why are the energy firms paying interest on this pile of customer cash?
We've discovered there is a gap in the rules, with no legal obligation on energy firms to pay interest on all this money they owe customers.
British Gas does not pay interest. The company said they use it to offset other customer debts.
E.ON does not pay interest either. They told us: "Normally only balance owed is refunded”.
Npower, EDF and SSE all do not pay interest.
We raised this with the industry watchdog Ofgem who told us it would expect firms to pay interest if they profited from having the money.
More top news
A service to remember 'Operation Dynamo', the code name for the mass evacuation of allied troops in 1940, will take place on the beach.
The Bank of England has launched a secret project looking at the economic risk to Britain if the country votes to leave the European Union.
The actress and The Only Way Is Essex star Mark Wright will become husband and wife over the Bank Holiday weekend.