Fraudsters are "cloning" phone numbers used by the taxman and calling people in a scheme to rip them off, police and fraud experts have warned.
The official income tax helpline for Her Majesty's Revenue and Customs (HMRC) is being used to threaten victims by claiming warrants have been issued for their arrest because of unpaid taxes.
People who use the web to check the number – usually 0300 200 3300 – are finding the top Google result confirms it belongs to HMRC.
Some phones will automatically display the number as "HM Revenue & Customs".
Despite the apparently legitimate number, the call is actually from fraudsters.
WARNING If you receive a call or recorded message from 0300 200 3300 claiming to be from HM Revenue with a warrant for your arrest due to unpaid taxes, put the phone down and DO NOT respond – THIS IS A SCAM! #hereforyou
— Crewe Police (@PoliceCrewe) October 30, 2018
A growing number of complaints and warnings on social media from victims and police suggest that some people are being fooled.
Scammers have often left voice messages and emails pretending to be from HMRC, but the number "cloning" tactic could be enough to persuade some people to transfer money.
An HMRC spokesperson told Sky News: "We will never call you out of the blue asking for money. If you're in doubt, you can put the phone down and call us back."
"This type of fraud, known as 'number spoofing', works by fraudsters cloning the telephone number of the organisation or person they want to impersonate, which in some cases can be the HMRC," said a spokesperson for Action Fraud.
"The fraudsters will then gain the person's trust by highlighting the number to them, claiming that this is proof of their identity, before trying to scam them in various ways.
"Never assume that someone is who they say they are just because their number matches that of an organisation or person you know.
"If someone tries to draw your attention to the number on your caller ID display, you should immediately become suspicious," said the Action Fraud spokesperson.
Communications regulator Ofcom is working with the Information Commissioner's Office to tackle nuisance and fraudulent calls, as well as the technical ways in which people can imitate numbers.
Spoofing a phone number is possible due to the use of Voice over Internet Protocol (VoIP) technologies, which make it very easy for callers to falsify their numbers and difficult for authorities to prevent.
The global Internet Engineering Task Force (IETF) is currently working to develop a new technical standard to ensure that the caller has to authenticate that they are the legitimate user of the number they are presenting as calling from.
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New Ofcom rules regarding CLI (Calling Line Identification) facilities came into effect last month, and require communications providers to identify and block calls which are misusing the CLI as part of fraud schemes.
:: Anyone who believes they have been targeted by this scam can report it to Action Fraud on 0300 123 2040 or by using the online fraud reporting tool