Small businesses are getting a "raw deal" from electricity and gas suppliers, according to figures released yesterday by the UK energy watchdog Energywatch.
And British Gas was named as the worst offender, as more and more companies looked to switch suppliers in an attempt to reduce costs.
The number of billing complaints every month from small companies increased by 22 per cent this year as companies sought advice on billing problems, Energywatch said in a statement.
And small business owners cited poor billing and disputes over contract renewal as the biggest source of problems with electricity providers.
In a customer satisfaction survey carried out for Energywatch earlier this year, none of the "big six" suppliers were rated by business owners as giving a satisfactory service.
And billing problems accounted for nearly two thirds of all the complaints made to the watchdog.
Energywatch has released league tables revealing the number of complaints it has received for each company as an information tool for customers wishing to switch supplier.
The group received the fewest complaints from Scottish & Southern Energy small business customers, and the most from customers of Centrica's retail arm British Gas Business.
Energywatch said it was six times more likely to be contacted with a problem from British Gas small business customers than from SSE customers.
Paul Savage, Energywatch business service manager, said: "The findings highlight widespread dissatisfaction among small businesses when it comes to their electricity suppliers. More than 2,000 businesses contact Energy-watch's business team each month for help in resolving problems with their energy supplier.
"Calls are on the increase as more and more small businesses seek help and advice. A staggering 90 per cent of calls come from small businesses that have had a raw deal from their energy supplier and need help to resolve disputes about billing, transfers or the way a contract has been sold to them.
"Until now, small businesses have been starved of information to help them compare suppliers. Our league tables should empower consumers and spur suppliers on to improve their customer service. Companies languishing at the foot of the league tables have much to do and those enjoying top spots will want to retain their positions."
Stephen Alambritis, of the Federation of Small Businesses, said: "With the publication of this information, Energywatch has exposed the poor standards of service meted out to our members.
"We will certainly be encouraging them to check it out when they are looking for a new supplier and will continue to support calls from Energywatch for regulatory protection to small businesses."