The Department for Work and Pensions (DWP) has issued an update to state pensioners who could miss out on the Winter Fuel Payment despite being eligible.
The change, announced in September, will see Winter Fuel Payments become means-tested, leaving millions without the crucial £300 support.
The DWP is now taking steps to contact eligible pensioners to ensure they don't miss out on the payment.
The Government department said it will get in touch with those claiming Housing Benefit but not Pension Credit.
The outreach is set to begin in November, as confirmed by DWP minister Sir Stephen Timms in response to Labour MP Paula Barker.
A DWP spokesperson stated: "We will be writing to 120,000 pensioner households in receipt of Housing Benefit but who are not currently claiming Pension Credit as they may be eligible.
Around 50 per cent of pensioners will heat their home less this winter
Getty/PA"We urge anyone who thinks they may be entitled to Pension Credit to check their eligibility and apply."
In London alone, an analysis by Age UK London revealed that approximately 127,000 pensioners are at risk of losing their Winter Fuel Payment despite being eligible to keep it.
These individuals, comprising 13 per cent of the city's 979,000 pensioners, are eligible for Pension Credit but are not currently claiming it.
The DWP is also collaborating with local councils to boost Pension Credit uptake.
Timms added that in the long term, the DWP aims to combine the administration of Pension Credit and Housing Benefit "as soon as operationally possible".
Under the new eligibility criteria, the Winter Fuel Payment will only be issued to those on specific benefits such as Pension Credit.
This change is expected to reduce the number of recipients in England and Wales from 10.8 million to 1.5 million.
In London, the impact is significant. Age UK London's analysis shows that about 636,000 pensioners - 65 per cent of the city's total - will lose their Winter Fuel Payments as they fail to qualify under the new rules.
The capital has a higher proportion of older people living in poverty compared to the rest of England. For instance, 25 per cent of Londoners aged 80-84 are in poverty, versus 19 per cent in the rest of England.
Claiming Pension Credit is crucial for pensioners to unlock various benefits, including the Winter Fuel Payment. The benefit is worth an average of £3,900 per year and acts as a gateway to other perks such as free TV licences for those aged 75 or older.
Age UK London is urging all struggling London pensioners to check their eligibility. They can contact their local Age UK or call the charity's helpline on 0800 678 1602, open 365 days a year from 7am to 8pm.
Mayor Sadiq Khan has extended his campaign to raise awareness about Pension Credit entitlement, helping Londoners claim over £17 million so far.
Pensioners can check their eligibility by calling the Pension Service helpline on 0800 99 1234 or using online calculators. Those in Northern Ireland should contact the Pension Centre on 0808 100 6165.
