Around 140,000 British households have been left without gas or electricity in the last year because they cannot afford to top up their prepayment energy meter, a charity has found.
Citizens Advice said the vast majority of these households - around 120,000 - included people who could be vulnerable, such as children or those with a long-term health condition.
Of all the households that lost their supply because the money on their meter ran out, 50% included someone with a mental health condition, 33% had a young child and 87% were in receipt of benefits, the charity found.
Just 9% contacted their supplier to discuss the issue.
The charity said more needed to be done to ensure people were aware that many suppliers now offered access to discretionary credit.
It is calling for a series of measures to ensure potentially vulnerable households at risk of losing their supply are more easily identified and prevented from having to live in cold and dark homes.
Citizens Advice chief executive Gillian Guy said: "It unacceptable that so many vulnerable households are being left without heat and light.
"For some people self-disconnection is easily managed, but for many others it is an extremely stressful experience that can have harmful physical and emotional effects.
"While some suppliers are now offering support to prepayment meter customers, industry and the Government need to do more.
We need better mechanisms to identify vulnerable customers, better coordination between suppliers and government agencies and we need suppliers to ensure that when people's health is at risk alternative ways to pay are offered."
A Department for Business, Energy and Industrial Strategy spokesman said: "This government is committed to tackling fuel poverty, with over five million consumers now protected by the safeguard tariff cap.
"The implementation of the Digital Economy Act later this spring will allow better use of Government data to make it easier for suppliers to identify vulnerable customers at risk of fuel poverty."