Insights Ofcom publishes Statement on Improving the accuracy of Calling Line Identification (CLI) data


Ofcom explains that a common tactic used by scammers is to “spoof” telephone numbers to make them appear to be from a trusted person or organisation, such as a bank. Where scam calls appear trustworthy, it means victims are more likely to share personal information or make a payment, which can lead to significant financial and emotional harm.

In February 2022, Ofcom consulted on proposals to strengthen its rules and guidance for providers to identify and block calls with “spoofed” numbers. Ofcom has now published a Statement setting out its final decisions on changes to the General Conditions (GCs). It has also published supporting guidance for telecoms companies on how to prevent scammers accessing valid phone numbers.

Ofcom has decided to modify GC C6 to require providers, where technically feasible, to identify and block calls with CLI data that is invalid, does not uniquely identify the caller, or does not contain a number that is dialable.

It has also decided to make various changes to its guidance for providers on what Ofcom expects them to do to comply with the rules in GC C6. This includes:

  • clarifying that the format of a CLI should be a 10- or 11-digit number;
  • making use of information that identifies numbers which should not be used as CLI, such as Ofcom’s numbering allocation information and the Do Not Originate (DNO) list;
  • identifying calls originating abroad that do not have valid CLI and blocking them;
  • identifying and blocking calls from abroad spoofing UK CLI; and
  • prohibiting the use of 09 non-geographic numbers as CLI.

Ofcom has decided that both the changes to GC C6 and CLI guidance should come into force six months after the date of the Statement’s publication, i.e. on 15 May 2023. This is to allow providers sufficient time to make the necessary technical changes. To access Ofcom’s Statement and for links to the guidance, click here.