The managing director of British Gas apologised today for problems caused by a new billing system which have led to a surge in complaints from customers.

Phil Bentley admitted the new system, which has led to thousands of consumers disputing their bills, had "teething problems" but insisted the situation is improving.

He said British Gas, which has been criticised for its "chaotic" customer service when people have attempted to complain about their bills, is working hard to improve services.

"Obviously we apologise for the inconvenience and the stress. I understand what it’s like to get a bill that’s incorrect. We apologise to those customers and we’re working very hard to improve services," he told BBC Breakfast.

"We have put in a new system. It’s working, but there are some teething problems."

Between October 2006 and last month, the company had 21,427 customer complaints, more than double the amount for the same period last year, when there were 8,012, an energy watchdog said.

According to Energywatch, last month alone more than 14,000 people complained. Mr Bentley disputed that figure, saying it was 3,000, but admitted that was 3,000 too many.

The majority were from customers disputing their bills, including problems with incorrect meter readings and out-of-date account details, Energywatch said.

Problems have occurred because customers are receiving estimated bills for greater amounts of gas or electricity than they are actually using, Energywatch says.

Instead of having their meters read, customers are sent a bill, calculated by a computer, estimating how much they have used.

Energywatch campaigns manager Adam Scorer said the problems, which also affect Scottish Gas, had arisen after British Gas started transferring customer accounts from one database to another.

"When customers have tried to complain about the inaccuracies in their bills, they haven’t been able to get through to a British Gas person on the phone," he told BBC Radio 4’s Today programme.

"Sometimes it takes them an hour and they have to come back time and time again before they get any sort of outcome.

"The inability to treat their customers who have a genuine problem with their bills with the most basic level of customer service is what’s causing British Gas’s reputation, quite frankly, to be dragged through the mud."

Mr Bentley, who started work last month, said British Gas had put on an extra 800 frontline staff in the last six weeks and the average wait to speak to an adviser is now 70 seconds - with a target of 60 seconds.

"I’m not saying we are there, but we are getting there," he said. "We are apologising to customers, but also recognising we are getting there and with some patience I’m absolutely confident we will get there by summer."

But Karl Brookes, a spokesman for Energywatch, said the company had failed to tackle serious problems with the way it handles customer service.

He said: "Energywatch reported six months ago that British Gas had the worst customer service in the industry.

"Since then their service has slumped from bad to worse."

He added: "The events that led to chaotic customer services from British Gas could have happened to any company.

"What consumers find unforgivable is the firm’s failure to deal with their problems and turn it around, despite promises to do so.

"Whilst some would say it’s a textbook example of why you should not carry on digging when in a hole, the impact this indifferent approach to customer service can have on consumers is not funny."

Mr Brookes added: "Customers should not be left hanging on the phone or having to explain their circumstances to several different advisers, time after time."