Increasing numbers of small and challenger energy suppliers are delivering poor customer service.

That’s according to Citizens Advice’s latest energy star rating league table, which is based on data gathered from 35 gas and electricity supply firms between October and December last year.

It scored Outfox The Market, Eversmart Energy, PFP Energy, Pure Planet and iSupply an overall score of less than two out of five – in the previous three-month period just one company scored this low.

Citizens Advice says problems include direct debits increasing without explanation, customers being unable to contact suppliers, unexpected changes in tariffs and large unexpected bills.

At the other end of the table, 21 of the 35 firms evaluated now score at least three out of five stars, up from 19 companies out of 34 in the previous rankings.

The consumer group has called for Ofgem to tighten rules on who can get a licence to supply energy, crack down on poorly performing firms and reduce the cost of suppliers exiting the market – it claims supplier failures in the past year alone have left other customers having to pick up the tab for an estimated £160 million.

Gillian Guy, Chief Executive of Citizens Advice, said: “The regulator needs to take urgent action by tightening rules around supplier licences, monitoring existing firms more closely and enforcing standards where these aren’t met.”

Energy UK’s CEO Lawrence Slade said: “In an increasingly competitive market, good customer service is just as important as price for many customers choosing their energy supplier.

“With 11 suppliers having exited the market since the start of last year – many of whom struggled with their customer service as well as financially – we agree that Ofgem needs to toughen the requirements for new and existing suppliers.”