Citizens Advice has called for new entrants to the energy market to face greater scrutiny.

The call comes as Ofgem has opened an investigation into small supplier Iresa. It is considering whether the company has broken rules on billing, complaints handling, customer transfer blocking and customer service.

Gillian Guy, chief executive of Citizens Advice, said: “According to our complaints-handling data, Iresa is one of the poorest-performing energy companies.