Fuel poor could miss out on help
The BBC has learned that not everyone eligible for the new Warm Home Discount will receive it because of funding limits.
Warm Home Discount replaces the current social tariffs provided by the energy firms to help customers on low incomes.
More than half a million pensioner households will get £120 off their bills this winter.
But other people suffering fuel poverty may miss out because of caps imposed by other energy companies.
While many pensioners qualify automatically for fuel poverty subsidies, other people have to satisfy a number of other criteria.
To be eligible most firms require customers to be in receipt of a means tested benefit, and either have a child under 5 or in receipt of disability benefit.
But Radio 4's Money Box has learnt that the companies set limits on the number of people they are prepared to offer subsidies to.
EDF Energy will offer subsidies to about 45,000 of its customers.
And according to EDF energy policy manager Valentine Mulholland, it will be a case of "first come, first served" for the rest.
Four of the other "big six" energy companies which Money Box spoke to said they too would be capping their fuel poverty funds.
Scottish and Southern Energy said it would help a minimum of 4,800 customers, although it expected to be able to help more.
However British Gas has a broader set of criteria than the other companies.
It is inviting applications from customers who have a household income of below £16,190 and spend more than 10% on fuel for adequate heating.
Ian Peters, the managing director of energy at British Gas, told Radio 4's Money Box programme "no eligible customer" would lose out:
"If they apply before the end of January for the first year, then I would have every confidence that they would get £120. I will guarantee we'll pay them," he said.
Jonathan Stearn of Consumer Focus said he welcomed the move by British Gas to help all those eligible, but other companies needed to do more.
He said: "If energy firms are able to offer help to more people, as British Gas has said it will be doing, this would clearly be welcome.
"But there is a wider issue of how to fund helping more vulnerable households. This needs to be tackled as part of a comprehensive fuel poverty strategy."
BBC Radio 4's Money Box is broadcast on Saturdays at 1200 BST, and repeated on Sundays at 2100 BST.