Sir Keir Starmer’s government faced accusations of trying to hide from the “horrific” impact of the decision to strip winter fuel payments from millions of pensioners.
More than 80% of people aged 80 and over will lose out, as will more than 70% of pensioners.
Even among those who should still receive the payments, worth up to £300, an estimated 780,000 will miss out because they have not claimed pension credit.
The figures were quietly slipped out on Friday night, which shadow Treasury chief secretary Laura Trott said was a “downright disgrace”.
Downing Street has said that a full impact assessment of the change, coming into effect this year, has not been carried out.
The Department for Work and Pensions released figures, published in response to a freedom of information request, are based on “equality analyses” which “are not impact assessments and not routinely published alongside secondary legislation”.
From this winter, only people on pension credit or certain other benefits will receive the payments, while about 10 million others are set to be stripped of the allowance.
The Government has insisted the move is necessary to help fill a “£22 billion black hole” in the public finances inherited from the Tory government.
Around 71% of those with a disability and 83% of those aged 80 or over will now miss out on the payment.
However, in its FOI response, the DWP said that while those with a disability will be disproportionately likely to retain the payment, “around 71% – 1.6 million – of people with a disability will still lose entitlement”.
And about 880,000 people currently set to lose the benefit this year are pensioners entitled to pension credit who have not claimed it, according to the analysis.
The assessment assumes a five percentage point “loss aversion” increase in pension credit take-up, which the DWP said then cuts the number of eligible pensioners failing to claim to about 780,000.
The DWP said: “The Government has followed its legal and statutory duties ahead of introducing these changes and will continue to do so.”
Ms Trott said: “The publication of these analyses is a damning indictment of this entire Labour government.
“Not only do these reports confirm that thousands of pensioners will suffer this winter as a result of Rachel Reeves’ cold-hearted decision, but they were also hidden until after Labour forced their MPs to vote through this cut.
“It is a downright disgrace.
“Labour have cut winter fuel payments for 10 million pensioners knowing the horrific impact it will have, but they will not be able to hide from the consequences of it. We will bring them to task every step of the way.”
The revelations have reignited a row over the policy, which has been attacked by both unions and opposition critics as it sets out to strip about 10 million pensioners of the support with their energy bills.
The Government has said the measures are expected to save about £1.3 billion in the first year.