HMRC's Voice ID database
It encourages the caller to say a key phrase instead of the conventional password to gain access to their accounts.
However, non-profit organisation Big Brother Watch warns that people have been 'railroaded into a mass ID scheme by the back door' and has reported HMRC to the Information Commissioner's Office (ICO) on the grounds that it has 'broken data protection laws'.
A Freedom of Information request revealed almost seven million taxpayers are enrolled in HMRC's Voice ID database of which 162,185 individuals have opted out and had their biometric data deleted by HMRC.
A spokesperson for HMRC said:
'Our Voice ID system is very popular with millions of customers as it gives a quick route to access accounts by phone.
All our data is stored securely, and customers can opt out of Voice ID or delete their records any time they want.'