The record of some of the worst energy suppliers in the UK keeps getting worse as the number of complaints continues to soar, figures released on Thursday (1 September) show.

According to charity group Citizens Advice, the gap between the worst and best performing energy suppliers is as wide as it has ever been, with a number of smaller suppliers attracting the ire of a lot of consumers.

The figures show that between April and June, small energy firm Extra Energy attracted a number of complaints 80 times bigger than that received by SSE, the best performing firm over the three-month period.

Extra Energy received 1,791 complaints per 100,000 customers, up from 1,682 in the previous quarter, while SSE received just 22 complaints per 100,000 customers.

"These figures reflect historic customer service issues that occurred during a period of time where Extra Energy saw our number of customers expand rapidly and unfortunately some of these complaints have taken longer than expected to resolve," said Ben Jones, Extra Energy's managing director of operations.

"We apologise unreservedly to anyone who has not received the standard of service we expect of ourselves."

EDF, British Gas and E.On were among the best-performing firms, while the Co-operative Energy and Scottish Power ranked second and third in the list of worst-performing suppliers.

The former saw the number of complaints grow from 819 per 100,000 customers to 850, while the latter's ratio increased from 558 to 571.

"The latest league table shows some suppliers are getting much better at sorting out their customers' problems, but it's disappointing to see others getting worse at dealing with complaints," said Gillian Guy, chief executive of Citizens Advice.

Claire Osborne, energy expert at uSwitch, said that while it was pleasing to see that some firms had worked hard to improve the relationship with their customers, others still had a lot of work to do to cut the number of complaints.

"It's encouraging to see some suppliers stepping up their efforts to improve their processes, but it's clear that others still have some work to do if trust in the energy industry is to be restored," she said.

"Inaccurate bills, one of the main causes for complaints, are unfortunately much more common than we would like."