Energy suppliers need to do more to help vulnerable customers this winter, the industry's regulator has said, with "severe weaknesses" found in the practice of five suppliers.
Ofgem said failings included customers missing out on free gas safety checks, vulnerable customers not being offered the support they need, and ensuring those on prepayment meters are identified and supported.
Although some good practice was identified, all 17 suppliers need to make further improvements.
Good Energy, Outfox, SO Energy, TruEnergy, and Utilita were judged the worst by Ofgem.
Severe weaknesses mean it "either found that a significant proportion of the supplier's processes and policies were missing or inadequate, or their data indicated that they are not achieving good consumer outcomes".
Moderate weaknesses were found in E (Gas & Electricity), Ecotricity, Green Energy UK, Octopus and Shell.
This means the supplier "did not have some of the policies or processes in place that we would expect, or the training and guidance available to their staff was not at the level we considered necessary".
'Much more needs to be done'
"We may also have found some poor performance data," Ofgem added.
Minor weaknesses were identified in British Gas, Bulb, EDF, E.ON, Ovo, Scottish Power and Utility Warehouse. This means Ofgem did not find any evidence of significant concern.
Neil Lawrence, director of retail at Ofgem, said: "From eligible customers who are missing out on free gas safety checks through to companies not identifying vulnerable customers to be offered obvious support on the Priority Services Register, this robust review has highlighted that suppliers need to do more to support consumers.
"We welcome the cooperation from suppliers and action taken so far, and, although we are seeing some very good practice in parts of the industry, we can see there is still much more to be done.
"Most suppliers take the protection of vulnerable customers seriously, and several good initiatives to support customers have been launched recently."
"While it's encouraging to see the engagement on this Market Compliance Review, with some improvement actions already taking place, we've seen a number of failings across the board which need to be urgently addressed," Mr Lawrence added.
"It's going to be a very challenging winter for everyone, and customers must be confident they are getting the help and support they need.
"My message to suppliers today is simple - be proactive. Help your customers to know what support is available, and then deliver it."
Ofgem said suppliers have engaged positively with the process and, since receiving their indicative ratings in October, are taking swift action to make the improvements needed.