The Ombudsman’s findings come after years of campaigning by the Women Against State Pension Inequality (WASPI) and a number of individual complaints to the PHSO.
The findings highlight multiple occasions on which the DWP was alerted to failures in its systems for advising women of changes to the State Pension Age (SPA) introduced in legislation in 1995, which increased the SPA for women from 60 to 65.
The Ombudsman found that despite their own research from the early 2000s telling them of large gaps in knowledge of this change, the DWP did not do enough to ensure affected women were directly made aware of this change.
The Ombudsman made two findings of maladministration against the DWP because it failed to respond appropriately to its own research, and when it did decide to act it took over two years to do so.
Targeted mailings did not start until 2009, some 14 years after their SPA was changed, indeed some women did not receive direct notice until 2012, after a further change in the law increased their SPA to 66.
According to the WASPI Campaign, there are approximately 6,200 women in East Renfrewshire who were born in the 1950s,many of whom would have had retirement plans disrupted by late information from the DWP.
East Renfrewshire MP Kirsten Oswald said: "This damning report exposes multiple failings and instances of maladministration by the Department for Work and Pensions over many years.
"Women born in the 1950s suffered a huge injustice at the hands of the DWP, it is time the UK Government recognised this. and I will continue to back the WASPI women’s call for redress for this shocking maladministration."
A DWP spokesperson respnded: “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.”