Under 11,000 customers have been affected by a meter reading mistake.
Energy UK said that’s the number of customers that have either been charged too much or too little on their gas bills.
Earlier this month, Ofgem revealed an error was caused by a mismatch between the unit the meter was measuring gas consumption in and the unit recorded in suppliers’ back office systems.
The regulator told energy suppliers to work alongside Energy UK to refund affected customers.
The trade body said suppliers will redress those affected.
It added: “Where there has been an overcharge, a refund will be issued as soon as possible.”