The Department for Work and Pensions (DWP) failed to communicate changes to the state pension age to women with enough urgency, according to an ombudsman.
The Parliamentary and Health Service Ombudsman (PHSO) said the department failed to act quickly enough once it knew a significant proportion of women were unaware of the changes.
The 1995 Pensions Act equalised the state pension age for men and women.
The ombudsman said it had received a significant number of complaints about the way this was communicated by the DWP.
Many women said that they were not aware of the changes, and experienced significant financial loss and emotional distress, it said.
The PHSO said that from 2005 onwards, there were failings in the action taken by the DWP to communicate the state pension age.
The ombudsman said its investigation will go on to consider the impact these failings had and make recommendations to put things right for any associated injustice.
Amanda Amroliwala, Parliamentary and Health Service Ombudsman CEO, said: “After a detailed investigation, we have found that the DWP failed to act quickly enough once it knew a significant proportion of women were not aware of changes to their state pension age. It should have written to the women affected at least 28 months earlier than it did.
“We will now consider the impact of these failings, and what action should be taken to address them.”
The PHSO provides a complaint handling service for issues about the NHS in England and UK Government departments.
A DWP spokesperson said: “Both the High Court and Court of Appeal have supported the actions of the DWP, under successive governments dating back to 1995, and the Supreme Court refused the claimants permission to appeal.
“In a move towards gender equality, it was decided more than 25 years ago to make the state pension age the same for men and women.”
Tom Selby, a senior analyst at investments firm AJ Bell, said: “Millions of women were affected by increases in their state pension age originally put forward in the 1995 Pensions Act.
“It was reasonable for these women to expect the Government to provide as much information as possible to communicate changes which would have such a profound impact on their retirement plans.”
He added: “The ombudsman now plans to look at the impact this injustice had, which will undoubtedly lead to more pressure for a resolution.
“Given the parlous state of UK finances, calls in some quarters to compensate women affected in full – which could amount to six years of state pension payments – are likely to fall on deaf ears.”