What spoofing is
When you receive a call, the network passes on information about the caller, including the number to display. This is called Calling Line Identification, or CLI. Spoofing means making that information show a false or invalid number.
Ofcom’s description is blunt: a spoofed call can appear to come from your bank, HMRC, a delivery company, a government body or even Ofcom, when it is really from a criminal trying to get your personal details, passwords or money.
Why it works
People answer numbers they recognise or trust. Ofcom’s research found that in February 2025, 42% of phone users said they had received a suspicious call in the previous three months, and that people are more trusting of calls from UK mobile numbers: 26% said they were likely to pick up an unrecognised UK mobile number, against 9% for an international number with an unrecognised country code. That is why fraudsters based abroad often fake UK numbers.
What phone companies must block
- Since 15 May 2023, Ofcom’s rules require phone companies, where technically feasible, to identify and block calls whose caller ID is invalid, does not uniquely identify the caller, or is not a number that can be dialled. Ofcom’s guidance also tells them to use its numbering allocation data, and bans 09 numbers from being shown as caller ID.
- Phone companies must block calls from abroad that falsely display a UK landline number, apart from a few legitimate uses. Ofcom said in July 2025 that this work had led to a million calls a day being blocked.
- Calls from abroad showing a UK mobile number were long exempt, so that people roaming abroad could still call home. In 2025 Ofcom proposed that such calls should have their caller ID withheld unless it can be verified, and in October 2026 it said it had set out strengthened guidance to stop criminals abroad spoofing UK mobile numbers.
Even so, Ofcom says some faked calls might get through.
What checking a number can and cannot show
A check on this site tells you whether a number’s block is allocated to a phone company in Ofcom’s data. If it is not, no provider should be using the number, and a call displaying it is exactly the kind of invalid caller ID phone companies are meant to block.
If the block is allocated, that only tells you the number exists. It does not prove the call came from it, and it says nothing about who made the call.
How to check a call that looks genuine
- End the call and contact the organisation yourself, using a number from its official website or your statement, not one the caller gave you.
- Ask for a reference number and a call-back number, then look the organisation’s number up independently before using it.
- Talk to someone you trust before acting. Ofcom notes that scammers often try to discourage this.
- If you think the call was a scam, send the number in a free text to 7726.