Electricity suppliers in Northern Ireland could be forced to simplify their bills if they do not make them easier to understand, an energy watchdog has said.

Quotes and invoices sent to the 57,000 business customers in the region are currently far too confusing and need re-structuring, a senior official from the Utility Regulator told Stormont's Enterprise committee.

Shane Lynch, director of electricity at the regulator's office, said they intended to urge suppliers to make bill changes voluntarily over the coming two years.

"If we don't see it happen then we will have to take an intervention type action via imposing a licensing requirement," he said.

Mr Lynch and regulator Iain Osbourne were briefing committee members about the outcome of an inquiry triggered by customer complaints about a price rise last year. The increase in September 2009 had been scheduled as it marked the end of a nine-month period when a government rebate - that had seen bills drop by 30% - had been in operation.

Mr Lynch said the 17 complaints received by consumers after the prices went up again demonstrated suppliers and the regulator had not done enough to keep customers informed.

"All of us need to up our game in terms of customer communication," he said. "It's completely unacceptable that a customer gets a surprise, particularly a customer with a big bill."

The official said the inquiry had also highlighted that competition in the electricity market was still relatively immature a decade after it was opened up to all suppliers. He said many customers were potentially missing out on savings by not shopping around for the best quote.

Committee vice chair Paul Butler (Sinn Fein, Lagan Valley) noted there was sometimes little difference between prices and asked was there any proof that suppliers were "colluding" to fix rates.

Mr Lynch said while that was a possibility they had considered they had found no prima facia evidence of it taking place. But he said there was definitely a problem with how bills were set out, noting one complainant had described reading them as 'like wading through treacle'.