First Utility, Ovo Energy and Utilita are being scrutinised by Ofgem over their “poor handling” of customer complaints.

The regulator has opened compliance cases into the companies after carrying out its bi-yearly complaints handling survey.

Ofgem said it is also expanding recent compliance engagement on complaints handling performance with Scottish Power through a compliance case which includes the results of the survey.

In addition to the new compliance action, Ofgem also requires all other domestic suppliers surveyed – British Gas, Npower, Utility Warehouse, SSE, EDF Energy, Eon and Co-operative Energy – to provide improvement plans on how they will deal with complaints and provide appropriate updates.

Ofgem’s CEO has warned that the regulator will act against suppliers who “fail their customers”.

The survey of more than 3,000 complainants found that satisfaction has improved since the last survey in 2016, with a third (32 per cent) of domestic customers satisfied with how their complaint was dealt with, an increase of five percentage points from 2016 (27 per cent).

However, the survey found that the proportion of customers who are dissatisfied (57 per cent) remains higher than those satisfied with how their complaint had been dealt with.

The main contributors to high levels of dissatisfaction were the length of time taken to resolve the issue, not being kept up to date with the progress of the complaint and suppliers not providing complainants with a clear view of how long the resolution will take.

Dermot Nolan, chief executive of Ofgem, said: “Although the level of satisfaction about complaint handling has increased over the past two years, it is still unacceptably low. Some suppliers need to be doing considerably more to get the basics right and provide a service their customers deserve.

“We will be monitoring the level of all suppliers’ customer service performance particularly closely after announcing proposals to introduce a price cap to protect those on poor value default deals from being overcharged.

“We are ready to – and will – act against those who fail their customers.”

A spokesperson for Ovo Energy, said: “We are always open to improvements and are confident that through working with Ofgem we can continue to build on our extremely high standards and swift resolution of issues.

“We pride ourselves on great customer service and will be interested to receive the details of the customer responses from this survey, so that we can establish the reason for the scores.”

Ofgem stressed that the opening of these compliance cases does not imply the regulator has made any findings about non-compliance by the suppliers.

It will report “in due course” on the findings of its compliance engagement.