London British tax collectors say a new computer system has revealed that almost 6 million people have paid the wrong amount of income tax, and 1.4 million will be told to repay an average of 1,500 pounds ($2,300) each.
HM Revenue and Customs says 4.3 million people will receive a rebate.
The problem affects some of the 40 million people whose income tax is automatically deducted from their paychecks under a system known as Pay As You Earn.
The tax agency said Saturday its computers have found that 2 billion pounds was underpaid through the system over the past two years, while 1.8 billion pounds was overpaid.
Tax advisers say people who receive the tax demands should seek advice, because they may not have to pay if they can prove the mistake was not their fault.