The figures is equivalent to nearly 9,000 requests a week.
Royal London says more people should ask the HMRC to check their income tax position if they believe they have paid too much.
HMRC figures showed all types of repayment it made amounted to a total of £7bn in the tax year.
Royal London says that reasons for applying for a tax refund can include:
• Tax paid on interest received as part of Payment Protection Insurance (PPI) compensation payouts
• Pension payments
• Income from a life or pension annuity
• A self-assessment tax return
• Interest from savings or PPI
• UK income for foreign domiciled residents
Becky O’Connor, personal finance specialist at Royal London, said: “Nearly half a million people tried to get overpaid income tax back from HMRC in the last tax year.
“This goes to show it’s a good idea not to assume the taxman is always right about what he says you owe.”
Anyone who thinks they may have overpaid income tax on savings and investments can fill in the R40 form on the HMRC website and can claim a refund for up to four previous tax years in most circumstances.