Nearly one million people aged over 75 are living in poverty and more help from the government is needed.
The charity Independent Age states ministers should do more to make older pensioners aware they can top up their pensions with other benefits.
The report also suggests the income of those aged over 75 is, on average, £3,000 a year less than younger pensioners.
Pensions minister Baroness Ros Altmann said the government had run campaigns to encourage pension credit claims.
In its report, Independent Age defines the “poverty threshold” for a single pensioner as £182 a week before housing costs. For couples, the figure is £272 per week.
Independent Age’s chief executive Janet Morrison said the UK’s 11.8m pensioners could not be classed as “one group”.
She added: “It would be foolish to assume that inequality simply ceases to exist at retirement age, but that is exactly what some of the recent rhetoric around ‘intergenerational unfairness’ does.
“The ‘silent generation’ of older pensioners, renters and single women have missed out on many of the gains of recent years.”
These, the charity says, include pension credit, a benefit that tops up low income.
An estimated 750,000 over-75s are entitled to pension credit but are not claiming it.
There are 11.8 million pensioners living in private households in the UK, of whom 4.8 million are aged 75 and over, it claims.
An estimated 950,000 pensioners in this older age bracket live in poverty, according to the charity’s report.
The report is based on analysis of the Family Resource Survey for the financial year 2013-14 This was published by the government and National Statistics.
It includes private households, but does not include those living in non-residential settings such as care or nursing homes.
Baroness Altmann stated the government wanted pensioners to have the money they are entitled to.
“I am concerned if older people feel uncomfortable about claiming and we have tried to make the process easier. We’re committed to protecting people’s incomes in later life,” she said.
She also said the government had increased the value of the state pension and pension credit “significantly in recent years” together with offering such benefits as free insulation for homes and protecting winter fuel and cold weather payments for pensioners.
BBC social affairs correspondent, Michael Buchanan, says welfare cuts since 2010 have targeted people of working age at the same time as protecting the income of older people.
For example, the state pension has been subjected to a triple lock since 2010, ensuring it rises each year by the higher of inflation, average earnings or a minimum of 2.5{06aeb1921e0b802d2bd9c766bc98fb11cc6a46c2b0593ed9c88a0e29cf417a34}.
Independent Age is also asking for pension credit – which unlike the state pension, increases only in line with average earnings – to be subject to its own triple lock.
Source: BBC News