The Energy Advice Line has urged the Big Six suppliers to extend their My Energy Credit reimbursement scheme to business gas and electricity users.
Julian Morgan, managing director of the price comparison, switching and advice service, said the scheme, which helps consumers access money they are owed by previous suppliers, should also apply to non-domestic energy users.
The campaign launched last September and extended this month, helps customers around the UK find out about money that might be owed to them.
According to suppliers, millions of pounds have already been reunited with their owners. Experts estimate an average 3 million householders are owed an average of £50 each after closing an account that was in credit.