Let's Break it down
Thousands of savers across the United Kingdom are facing unexpected tax bills due to errors in HM Revenue and Customs’ (HMRC) automated systems. These mistakes, attributed to the way savings account data is processed, have led many individuals to overpay tax sometimes by several thousand pounds on their interest income.
In several instances, people have discovered that tax has been deducted from tax-free ISA accounts or even from non-existent savings, placing additional strain on household finances. This development comes as financial advisers and industry experts warn of growing concerns regarding the reliability of data sharing arrangements between banks and HMRC, with implications for the wider taxation system and consumer trust.
Overview of HMRC Savings Tax Errors
Recent reports highlight that HMRC has mistakenly charged thousands of savers tax on interest income that either does not exist or is generated within tax-exempt ISA accounts. The root of these errors lies in the automated exchange of savings interest data from banks and financial institutions, mandated by rule changes introduced in 2016 to streamline tax collection.
Under these rules, banks are required to send details of savings interest earned by customers directly to HMRC. The tax authority then uses this information to adjust Pay As You Earn (PAYE) codes and collect what it calculates as the correct tax owed. However, errors in the system ranging from double-counting interest to misattributing ISA accounts have become increasingly widespread, according to industry professionals.
How Financial Institutions Share Data with HMRC
Since 2016, financial institutions have sent annual savings interest data on their customers directly to HMRC. The intention is to make tax code adjustments automatic, reducing the administrative burden on both the taxpayer and the government.
However, errors in the data provided, or in the way HMRC processes it, can result in incorrect tax deductions. In some instances, as financial advice firm Shackleton has warned, automatic tax code adjustments are made “without any clear breakdown of how the figures have been calculated”. The system often relies on previous year’s figures, which may inadvertently penalise savers if estimates are inaccurate or outdated.
Impact on Taxpayers and Documented Mistakes
The consequences for savers can be significant. One documented case involved HMRC estimating a worker’s untaxed savings interest at £3,847, when the true figure was only £94. This led to the taxpayer overpaying £1,476 in the 2025-26 tax year, with a marked reduction in monthly income.
The situation was only rectified after the individual contested the calculation. In another instance, online bank Zopa, which has 1.7 million customers, revealed that hundreds of its clients had their tax codes wrongly adjusted because tax-free ISA interest was mistakenly reported as taxable. Despite Zopa alerting HMRC and sending corrected data on the same day, many affected customers continued to receive erroneous tax demands for some time afterwards. Error rates are reportedly increasing.
Financial advisers note a “growing number of cases” of clients being assigned incorrect tax codes or linked to savings accounts they do not own. Official data confirms that in the previous year, 2.76 million individuals were subject to savings income tax deductions.
Industry Reactions and Political Criticism
The issue has drawn sharp responses from across the political spectrum. Richard Fuller, shadow chief secretary to the Treasury, said, “At a time when many are struggling with tax increases and the cost of living, we are learning that HMRC has been taking money it should not, putting people’s finances under strain. Ministers should act to bring HMRC into line and stop these unnecessary charges.
” Former Conservative leader Sir Iain Duncan Smith echoed these sentiments, stating that HMRC had been “a department that has been a law unto itself for far too long.” Commentators have also raised concerns over HMRC’s access to bank data. Sir Iain added, “Spying on people’s private lives is not what I would call doing a good job.” Mike Warburton, a longstanding tax columnist, cautioned savers: “Individuals have got to wake up to the fact that you cannot trust what HMRC is telling you. You have to check it.”
HMRC’s Response and Planned System Changes
HMRC maintains that the tax authority relies on the most recent data provided by financial institutions to update codes for PAYE taxpayers. The official position is that HMRC “does not want anyone to overpay or underpay tax” and urges individuals to contact the department if inaccuracies are suspected, so corrections can be made.
To reduce future errors, HMRC has committed to verifying interest figures supplied by banks for 2025-26 in November of this year. Furthermore, from 2028, regulatory changes will require banks to collect National Insurance numbers from all customers and to provide quarterly rather than annual savings data to HMRC. The aim is to improve the accuracy and timeliness of reporting, streamlining the process for both banks and tax authorities.
Final Summary
The discovery of significant and ongoing errors in HMRC’s savings tax collection process has placed many UK savers at risk of overpaying tax unnecessarily. Industry experts and politicians have called for urgent reforms and better oversight to address automatic coding errors and inaccurate data handling.
HMRC acknowledges the problem and has outlined changes to improve data accuracy, including new reporting requirements for banks from 2028. In the meantime, savers are encouraged to monitor their tax affairs closely and contact HMRC if mistakes arise. You can also use Pie Tax to easily track your tax and ensure you aren’t overpaying.
