Gas flameMost customers who complain to their energy company are left dissatisfied, according to the industry regulator.

Ofgem said that not calling people back when agreed was an area requiring "critical improvement" by major energy firms. But the report did conclude that overall satisfaction has improved since a similar survey in 2010.

Scottish Power and SSE maintained their position as having the highest customer satisfaction for handling complaints, while EDF recorded the lowest score out of the so-called big six energy suppliers.

Almost half of people (48%) were left dissatisfied at the speed by which their complaint was resolved, with more than a third (35%) unhappy at not being called back as promised.

The Ofgem study also found that a high proportion of customers did not receive confirmation that a complaint was resolved.

"Expectations from customers are not particularly high or demanding of energy suppliers, but in most cases these expectations are not being met in terms of communications relating to the resolution of their complaint," the report concluded.

Just over 3,000 customers who had made a complaint in December last year were interviewed for the research.

Audrey Gallacher, director of energy at Consumer Focus, described the overall improvement as positive but declared there was "still a very long way to go".

She said: "The energy industry routinely tops the charts as the sector least trusted by consumers and the customer service they receive is a significant factor in this.

"It is unacceptable that many customers have to go through a long, drawn-out process to get their problem resolved. There must be clear progress on this from suppliers. Ofgem has outlined moves needed by suppliers and the regulator must now ensure these improvements are delivered."