The Department of Work and Pensions has admitted it does not know how many people it owes money to, after paying out more than £130,000 to one pensioner.
People should not expect the agency to remind them to claim money they are owed, according to financial firm, Responsible Life.
One Responsible Life customer, Peter Williams, was handed £138,000 in back payments from his state pension.
Although he had filled out the forms to claim the £168.50 per week pension payments 11 years ago, he heard nothing back and assumed he was ineligible.
After struggling to live on his savings alone, Williams contacted Responsible Life who discovered the astonishing amount of money he was owed by the government.
Responding to an FOI request made by the equity release firm, the DWP said it does not hold data on people who have not claimed their state pension, or how much money those people are owed.
It also said that while notifications are sent four months before someone becomes eligible for the state pension, they do not issue reminders to people after that point.
‘It sickens me’
Responsible Life managing director Steve Wilkie told the Mirror, “Any number of people who have reached state pension age could be missing out on millions of pounds.
"It sickens me to think of the sacrifices some will be enduring to make ends meet, unaware that those hardships are completely unnecessary.
“We will never know much money is collecting in the government’s coffers instead of being returned to people who have contributed all their lives but it’s time the government did the right thing.
“We have seen first hand how windfalls are waiting for those who have not claimed their state pension for a variety of reasons.
“Reminding people that they are entitled to a state pension is the responsible and the right thing to do.”
A Department for Work and Pensions spokesman said, "There is no legal requirement for DWP to notify people, either individually or generally, about eligibility for state pension; however, DWP provides a claim invitation to ensure as many citizens are prompted to claim. Reminders are not issued.
"We want everyone to be able to claim what they are entitled to and have a wide range of channels where people can get information and advice."