UK Phones Providers Introduce Tougher Blocking of Foreign Scam Calls

Ofcom has confirmed that, from today, UK phone providers (fixed line and mobile) are expected to have implemented changes that aim to block scammers who call from abroad and imitate UK landline numbers (i.e. spoofed calls). Further measures are also expected to follow “later this year“, which will tackle spoofed mobile numbers.

Just to recap. Most of the United Kingdom’s major broadband, phone and mobile providers have already implemented various technical measures to tackle Nuisance Calls and Scam Calls. But these aren’t always 100% effective, and not all operators have introduced the same level of protections. Suffice to say, there’s still plenty of scope for improvement.

NOTE: There are generally two numbers associated with an incoming call: the Network Number, which identifies where the call is being made from; and the Presentation Number, which identifies who is making the call.

Back in 2022 Ofcom moved to further clampdown on such calls by requiring all telephone networks involved in transmitting calls – either to mobiles or landlines – to identify and block spoofed calls, albeit only “where technically feasible” to do so (here). The move improved the accuracy of Calling Line Identification (CLI) and they also made it harder for scammers to access valid phone numbers by introducing additional checks.

Despite the improvements, scammers who call from abroad could still spoof their number to make it look like the call has come from a trusted UK-based organisation or person, when in fact they are actually calling from another country. Calls like this are naturally more likely to be answered, and thus Ofcom set about working with the industry to impose stricter measures against “Presentation Numbers”.

The Network and Presentation Number are usually the same, but there are some scenarios where a caller may wish to display a different number to the line the call is being made from. For example, an outsourced call centre that makes calls on behalf of different businesses, or businesses which may wish to display a single number for outbound calls.

Ofcom’s approach was to update their CLI Guidance so that phone providers are now expected to identify and block calls from abroad that use a UK geographic or non-geographic telephone number as a Presentation Number, except in a limited number of legitimate use cases. This removes a loophole through which scammers can spoof a UK number from abroad. Ofcom previously gave the industry until 29th January 2025 (today) to implement this.

Marina Gibbs, Policy Director for Networks and Communications, said:

“Today’s strengthened industry guidance will help to further disrupt a common tactic used by fraudsters operating from abroad, as any calls which falsely display a UK landline telephone number should be blocked from getting through.

With further measures to tackle spoofing of UK mobile numbers being announced later this year, Ofcom will continue to play our part alongside the police, other regulators and the telecoms industry in the collaborative effort to protect consumers against scams.”

Some operators, such as BT, already implemented this change last year on a voluntary basis, which resulted in around 1 million calls per day being blocked from entering their network within the first month of operation. The fact that this has today become a standard practice should thus have a significant impact upon the problem, provided it’s being properly implemented by all.

Ofcom are currently working on technical solutions for extending a similar measure to tackle spoofed mobile numbers (here and here). The regulator is expected to set out their preferred approach to this sometime later this year (around spring), which will require another industry consultation and then an implementation phase (i.e. it’s likely to be early to mid-2026 before this is introduced).

The challenge in all of this invariably stems from the inherent problem of implementing such rules without also over-blocking legitimate voice calls and messages, which is easier said than done – particularly at a time when the UK is in the middle of a transition from analogue to IP-based (digital) phone services. But this should become easier once all such services have gone digital (IP-based) as new methods will then become viable (e.g. CLI Authentication [CLIa] – here).

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