Ofcom UK to Restrict Number Spoofing to Tackle Mobile Scam Calls from Abroad

The UK internet content and telecoms regulator, Ofcom, has today proposed changes that will require phone providers to withhold the Caller ID (CLI) of calls that appear to come from a UK mobile roaming abroad unless they can verify its validity. The goal is to tackle scam calls by cracking down on number “spoofing“.

Just to recap. Most of the country’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, and so Ofcom have been gradually introducing further changes.

For example, at the start of 2025 the regulator implemented changes that aimed to block scammers who call from abroad and imitate UK landline numbers (i.e. spoofed calls), which imposed stricter measures against “Presentation Numbers” (here). The move was useful because otherwise potential victims might trust a UK number more than an international one, and thus related calls are more likely to be answered.

However, the above change only worked for landlines, and today’s new proposal is intended to extend that to tackle spoofed mobile numbers. This is because there is currently an exemption from blocking calls from abroad that display a UK mobile caller ID, which exists to allow people who are roaming abroad to display their number to family and friends when they call them.

Ofcom’s research reveals that, in February 2025, 42% of phone users said they received a suspicious call in the last three months and people are more trusting of calls coming from UK mobile numbers (+447) than they are of calls from withheld or international numbers. Some 26% said they were likely or very likely to pick up a call from an unrecognised UK mobile number, compared to just 9% who would answer a call showing an international number with an unrecognised country code.

Marina Gibbs, Ofcom’s Policy Director for Networks and Communications, said:

“Customers endure a barrage of scam calls, and when people get caught out, the consequences can be devastating. It can happen to anyone, with criminal gangs in other countries trying to exploit people when their guard is down.

The work we’ve collectively already done has led to a million calls a day being blocked, but there’s no silver bullet, and we’re always looking for new ways to shore up our defences in the fight against fraud. These new measures would provide further protection for people in the UK.”

Ofcom’s Proposal

UK communications providers should withhold the Presentation Number of calls that appear to come from UK mobile users roaming abroad, except where they can verify the validity of the caller.

We are proposing to amend our CLI Guidance to set out how we expect providers to process calls from abroad that appear to come from UK mobile (+447) numbers.

When these calls first reach a UK provider (including entities acting as international gateways), the provider should modify the call’s CLI data to mark the CLI Presentation Number as ‘withheld’.

UK providers should have arrangements in place with their roaming partner networks so that calls to the UK that their customers make while roaming abroad are routed via the customer’s ‘home’ network (i.e. the network of the UK provider in question). After the call’s Presentation Number is marked as withheld, the home network should then modify the CLI data of calls from customers who are genuinely roaming abroad, so that the call recipient can see who is calling them, where technically feasible (and unless the caller has elected to withhold their number).

This two-step process will remove the ability of scammers outside the UK to present a spoofed UK mobile (+447) Presentation Number to people and businesses in the UK. This is because no home network will be able to verify the validity of these calls and therefore the Presentation Number will appear as withheld.

We expect the effect of this measure to be that UK people and businesses receive significantly fewer calls from scammers that appear to come from UK mobile users, although scammers may still be able to send messages from UK SIMs which they manage to source and use from overseas destinations. In turn, this will reduce the likelihood that people engage with scam calls and lose money.

Ofcom intends to consult on this until 13th October 2025 and will then publish their final decision during “early 2026“. After that, UK mobile operators would be given 12 months to introduce the changes, which is needed to “give providers the opportunity to modify agreements with roaming partner networks to have their customers’ calls routed via the UK provider’s network, where such agreements are not already in place“.

The challenge in all of this invariably stems from the inherent problem of implementing such rules without also over-blocking legitimate calls and messages. 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).