Under the Ofgem order, Iresa is banned from taking on new customers, one off payments and increasing direct debits until further notice.

The move comes after the supplier failed to resolve its customer service issues since Ofgem imposed a temporary ban in March this year.

Targets were set for Iresa to improve its customer service offering. If they were met in a three-month period, Ofgem would lift the ban.

Iresa were told to extend call centre hours, improve call waiting times and respond to customer emails faster.

While Iresa has reduced its call waiting times from the 40-minutes reported by customers, Ofgem said it “has not made enough progress in reducing the backlog of customer emails”.

Further, Ofgem said that Iresa is starting to “show signs of improvement in how it handles complaints” and “manages vulnerable customers”, but this is “not good enough”.

The ban extension will remain in place until the Nottinghamshire-based firm implements significant improvements.

If it fails to meet these objectives, Ofgem has the power to revoke Iresa’s licence.

Dermot Nolan, chief executive of Ofgem, said: “Iresa continues to let its customers down by failing to provide a level of service its customers deserve.

“Although it has made some improvements since we issued the provisional order in March, the supplier has been unable to meet all the requirements we set it three months ago to get its house in order.

“Ofgem will step in to protect consumers if any supplier fails to provide a satisfactory level of customer service and will take firm action against those flouting the rules, which could include a supplier’s licence being taken away.”

Separately today, charity Citizens Advice named Iresa as the worst energy company for customer service amid record complaint levels. The firm scored just 0.35% stars out of a possible five stars for customer service between January and March this year.

Citizens Advice said it received the “worst-ever complaints score recorded” as it notched up over 9,000 complaints per 100,000 customers – five times higher than the next offender, TOTO Energy which received 1,800.

Firm So Energy came top, scoring 4.8 stars while SSE was the best performing of the ‘Big Six’ energy suppliers (British Gas, EDF, E.ON, Npower, Scottish Power and SSE).

Iresa did not reply to requests for comment.