Mistakes by officials saw pensioners across the UK underpaid by £530 million last year, according to Government figures.
Analysis of the figures by the Labour Party found more than one in 10 pensioners – around 1.3 million people – did not receive their full benefit.
That amounted to almost half of mistakes which saw benefit claimants miss out on £1.1 billion during the 2021-22 financial year.
Labour said around 1.8 million people had been underpaid due to processing errors by the Department of Work and Pensions (DWP), HMRC or local authorities.
Shadow work and pensions secretary Jonathan Ashworth said: “When so many families and pensioners are struggling, these levels of incompetence are staggering.
“It’s time blundering Tory ministers got a grip.
“Labour would crack down on these failures and take action to get living standards up and tackle the growing poverty crisis facing the country.”
State pensions accounted for 48% of underpayments with Universal Credit recipients missing out on £140 million.
Employment and Support Allowance payments were out by £130,000 according to the figures.
Our priority is ensuring everyone receives the financial support to which they are entitled and, where errors do occur, we are committed to fixing them as quickly as possible
DWP spokesperson
The figures reflect the first year of giving figures based on checks rather than using estimates.
DWP figures released last month showed pensioners had received £300 million to counter underpayments.
A DWP spokesperson told the Daily Express: “State pension underpayment rates remain low at 0.5% of expenditure.
“Our priority is ensuring everyone receives the financial support to which they are entitled and, where errors do occur, we are committed to fixing them as quickly as possible.”
Initial government estimates for the 2022-23 financial year are due to be released on May 11.
