Millions more scam calls from abroad that use spoofed UK landline numbers are to be blocked after the telecoms regulator finally ordered a long-overdue clampdown.

From Monday all phone companies will have six months to identify and block calls from abroad that falsely display a UK telephone number under strengthened guidance from Ofcom.

Fraudsters around the world have been able to call UK consumers for years using what is known as a spoofed phone number – changed using a laptop to appear as if it were coming from a UK bank, government department or similar.

People answering often saw the same number on their handset as that used by their bank, and were frequently scammed after believing that they were talking to the lender’s fraud department.

The Guardian first highlighted how fraudsters were able to use spoofed numbers in 2019, at a time when most readers were unaware that a fraudster could hack the system to make it appear they were calling from another number.

It went on to feature and help a dozen readers who had collectively had £290,000 stolen from their bank accounts.

Ofcom has since been under pressure to act, but progress has been painfully slow. BT has prevented as many as 1m calls a day from entering its network on a voluntary basis since July 2022, and other firms such as TalkTalk have adopted similar measures.

Now the regulator has ordered the other telecoms firms to block “presentation” numbers, albeit with a further six-month grace period. That means fraudsters will still be free to call consumers on some networks until January.

Criminals stole £1.17bn through unauthorised and authorised fraud in the UK in 2023, much of it starting through a spoofed number phone call.

The Ofcom group director for networks and communications, Lindsey Fussell, said: “Criminals who defraud people by exploiting phone networks cause huge distress and financial harm to their victims.

“While there’s encouraging signs that scam calls and texts are declining, they remain widespread and we’re keeping our foot to the throttle to find new and innovative ways to tackle the problem.

“Under our strengthened industry guidance, millions more scam calls from abroad which use spoofed UK landline numbers will be blocked, with similar plans uunder way for calls which spoof UK mobile numbers. We’re also challenging the industry and other interested parties to provide evidence on the best solutions to tackle mobile messaging scams.”

Ernest Doku, a telecoms expert at the price comparison website uSwitch, welcomed the move. “With increasing mistrust around answering phone calls, consumers will welcome this development. Recent research from Uswitch shows that almost two-thirds of Brits don’t answer the phone because of concerns about scams or scam callers,” he said.

“While making changes like this can take time, Ofcom’s six-month timeline may mean a delay before we see a reduction in these types of phone scams, as the deadline for these stricter measures to be implemented isn’t until 29 January 2025.”