Nearly half a million taxpayers sought income tax refunds from HMRC in the 2018/19 tax year, according to insurer Royal London.
Royal London submitted a Freedom of Information (FOI) request, and revealed that 460,000 taxpayers chased HMRC for refunds in relation to overpaid income tax in 2018/19.
The insurer found that individuals changing jobs in 2018/19 and taxpayers being subject to changes to taxable benefits were the main reasons for tax being overcharged.
The FOI request revealed that the total value of repayments to taxpayers in 2018/19 was £5.1 billion.
Commenting on the data, Becky O'Connor, Personal Finance Specialist at Royal London, said: 'This goes to show it's a good idea not to assume the taxman is always right about what he says you owe.
'Always check your tax statement for the year and keep a note of any unusual changes to your income that might mean you have overpaid.'