The total number of complaints dropped from around 5 million in 2015 to 3.5 million in 2016 – the lowest number in three years.

Most large and medium suppliers solved at least 90% of complaints within eight weeks, the deadline after which complaints may be referred by individuals to the Energy Ombudsman.

Data released by the Ombudsman shows energy suppliers were required to ‘hand back’ £3.3m to consumers in financial awards last year.

In May 2015, the Energy Ombudsman introduced tougher penalties for suppliers that did not implement remedies within 28 days. It said this has led to a reduction in the time consumers have to wait for their awards to be implemented.

Ofgem CEO Dermot Nolan said: “Ofgem welcomes the overall fall in complaints since 2014.

“We are seeing clear signs that some suppliers are competing harder on customer service. This is good, as it puts pressure on poor-performing companies to up their game or lose market share.

“We want to see all suppliers to take steps to bring down complaints further. We take strict action where we see companies failing and have imposed over £50m penalties for companies for poor customer service.”