British energy suppliers have been failing vulnerable customers, the sector's watchdog has said, as people face a cold and costly winter.
Regulator Ofgem has ordered improvements after it found problems at all 17 firms which took part in a review.
But some of the suppliers hit back at the work, which they described as "incomplete".
Consumer groups described the regulator's report as "hugely concerning" at a time when people were being hit by bills double the level of last winter amid the soaring cost of living.
Ofgem said some of the worst examples of poor practice included suppliers failing to read the meters of customers who could not do so themselves.
It also found that some vulnerable customers were unable to contact their supplier to top up their meter or to request support credit.
Self-disconnected
In some cases, debt repayment rates were set so high that vulnerable customers self-disconnected - in other words, did not top-up their prepayment meter when the credit ran out.
The BBC says five suppliers - Good Energy, Outfox, So Energy, Tru Energy and Utilita - were found to have "severe weaknesses".
"Moderate weaknesses" were found at suppliers E (Gas & Electricity), Ecotricity, Green Energy UK, Octopus and Shell.
Ofgem said that seven others had shown minor weaknesses, including British Gas, Bulb, EDF, E.ON, Ovo, ScottishPower and Utility Warehouse.
Neil Lawrence, Ofgem's director of retail, said "most suppliers" took their responsibility to protect vulnerable customers seriously and added firms had launched new initiatives - including dedicated phone lines.
But he added: "We've seen a number of failings across the board which need to be urgently addressed.
Very challenging winter
"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."
It is Ofgem's third review into various aspects of suppliers' treatment of customers.
The first demanded action on soaring direct-debit demands and the second found more help was needed on payment plans for those struggling to pay.
This latest review required suppliers to give evidence about how they identified and kept records of customers in a vulnerable situation, and whether they were added to a priority register for help.
Suppliers also gave information about free gas safety checks and vulnerable prepayment meter customers.
All 17 suppliers which submitted data to the regulator were told they had to improve their practices.
Risks
Ofgem said that in general, there were risks that people were not identified as vulnerable and given the support they were entitled to.
But questions have been raised for the regulator itself, which has been accused of being asleep at the wheel when bills are soaring and suppliers failing.
In response, it said it had moved to proactive methods, rather than waiting for issues to be reported.