Scam calls from real-looking numbers: why caller ID can lie, and how to screen calls

What's happened

Ofcom has fined the telecoms provider Tismi £437,500 for failing to stop scammers misusing its phone numbers. The regulator said on 21 October 2026 that from at least November 2022 to January 2025, Tismi had no appropriate measures to prevent misuse, leaving about 366,000 numbers it had passed on to business customers open to scammers.

Ofcom found that Tismi handed out numbers without proper checks, didn't monitor whether they were being misused, and had no formal process for dealing with reports. The fine includes a 30% discount because Tismi admitted liability. Ofcom has also opened an investigation into another provider, Xtra Phones UK, over concerns that its numbers are being misused.

The same day, Which? reported that the Information Commissioner's Office received 3,684 complaints about automated nuisance calls in September 2026, up from 1,374 in July.

Why caller ID can lie

The number on your screen isn't proof of who is calling. Scammers can "spoof" a number so the call appears to come from somewhere else, including your bank's real phone number. Which? says fraudsters use this to pose as banks, HMRC and the police, and may use AI voice cloning to sound like someone you know.

Since January 2025, Ofcom has required phone companies to block calls from abroad that falsely show a UK landline number, and in July 2026 it said providers should withhold the caller ID of calls that appear to come from a UK mobile abroad unless they can check it's genuine. That helps, but it doesn't catch everything.

The warning signs

• A familiar number with an urgent problem. The screen shows your bank, and the caller says your account has been hacked.
• A request to move money to a "safe account". UK Finance's Take Five campaign lists this as a quick check for fraud.
• A request for a one-time passcode, password or PIN, or to read out a code that's just been texted to you.
• Pressure and secrecy. You're told to act now and not to tell anyone.
• A call from Ofcom. Ofcom says it never calls out of the blue or asks for bank details.

What it could cost: a worked example

This is an illustration, not a real case. Sam's phone shows his bank's customer service number. The caller says someone is trying to take money from his account and asks him to move his savings to a "safe account". Sam makes two transfers totalling £2,400 to an account the scammer controls.

Because Sam paid by bank transfer, he's covered by the reimbursement rules for payments made on or after 7 October 2024. The Payment Systems Regulator says banks must normally refund this kind of fraud, up to £85,000, within five business days of a claim, or up to 35 business days if they need more information. Banks may keep an excess of up to £100, but not from vulnerable customers. So Sam should get back at least £2,300. If he'd hung up and rung 159, he'd have lost nothing.

How to screen calls

• iPhone: Call Screening arrived with iOS 26. Go to Settings > Apps > Phone > Screen Unknown Callers and choose "Ask Reason for Calling", so unknown callers must say who they are before your phone rings, or "Silence" to send them to voicemail.
• Android: In the Phone by Google app, go to Settings > Caller ID & spam (or Spam and Call Screen) and switch on spam identification. Pixel phones have a "Screen call" button that shows a live transcript, and Samsung's Galaxy S26 phones have Call Screening.
• Landlines: Which? suggests a cordless phone with good call blocking, such as only letting through calls from contacts. It's especially useful for older relatives.

Silencing unknown numbers can mean missing a GP surgery or delivery driver, so check your voicemail regularly.

What to do if you get a call like this

1. Hang up. A genuine caller won't mind.
2. Call 159. It puts you through to your own bank, and Stop Scams UK says it covers more than 99% of UK current accounts. Or use the number on the back of your card.
3. Report the number. On a mobile, text the caller's number to 7726 for free. Ofcom says landline scam calls should be reported to Report Fraud. Forward scam texts to 7726 and scam emails to [email protected].
4. If you've lost money, tell your bank straight away, then report it to Report Fraud on 0300 123 2040 in England, Wales and Northern Ireland, or to Police Scotland on 101. You have 13 months to claim a refund for a bank transfer.
5. Cut down nuisance calls. Register free with the Telephone Preference Service, and report nuisance calls to the ICO.

Your questions answered

Can a scammer really show my bank's real number?

Yes. Ofcom's rules now block many overseas calls that fake UK numbers, but not all, so treat any unexpected call about your money with suspicion, whatever number it shows.

Will the Telephone Preference Service stop scam calls?

It helps with legitimate companies, but Which? warns that scammers ignore the rules. Call screening and blocking add a second layer.

Should I answer withheld numbers?

Some are genuine, such as a hospital. Ofcom's advice is to be cautious. If a withheld caller asks about money or personal details, hang up and call the organisation back on a number you've found yourself.

Sources: Ofcom: Tismi fined £437,500, Which?: how to screen calls, Ofcom: new rules on scam messages and spoofed mobile numbers, Ofcom: reporting to 7726, Take Five to Stop Fraud, Stop Scams UK: 159, Payment Systems Regulator