Ofgem opened an investigation into the group in February, saying it would, “examine whether Iresa broke rules relating to customer information and customer contact. This includes examining whether they treated customers fairly in their call handling and complaints processes.” Customers had reported wait times of 40-minutes for answering calls.

There were also concerns about how the group had dealt with vulnerable customers. The regulator is investigating whether the group gave indebted customers sufficient notice that they were taking a debt repayment out of their account, or established whether customers were able to pay the debt. Customers had reported unexpected increases in direct debit demands and an inability to log complaints

In addition to not being able to take on new customers, the Nottinghamshire-based firm cannot increase direct debits or ask for one-off payments for up to three months.

It must also extend call centre hours to bring down average waiting times to below five minutes, respond to customer emails within five working days, clear a backlog of consumer emails, log customer complaints, and create a priority services register for vulnerable customers. Ofgem has threatened to revoke Iresa’s licence if it doesn’t comply.

Dermot Nolan, chief executive of Ofgem, said: “This order sends out a very clear message to suppliers that where they fail their customers on service, Ofgem will step in and take strong action.

“It’s crucial that all suppliers provide customers with good service, including acting quickly and effectively to sort things out wherever problems occur.

“Iresa now needs to act quickly and put its house in order otherwise ultimately its licence could be revoked.”