Major phone networks have agreed to automatically block almost all internet calls coming from abroad if they pretend to be from UK numbers, Ofcom has confirmed.

Criminals have been using internet-based calling technology to make it look like a phone call or text is coming from a real telephone number.

So far, one operator has already implemented the new plans, the regulator told the BBC, while other phone networks are still exploring methods of making it work.

She added that tackling the phone scams issue was a "complex problem" that requires a coordinated effort from the police, government, other regulators and industry.

Internet-based calling technology, also known as Voice Over Internet Protcol (VoIP), is used by millions of consumers globally to make phone calls free or cheaply every year.

They say blocking traffic from foreign VoIP providers won't work to stop scam texts and calls, because much of the UK is still relying on old copper-based ISDN networks dating back to the 1970s.

Apart from consumers, many businesses also use the VoIP technology for internal corporate phone networks.

Whenever a corporate phone network makes a call, a VoIP provider hands over the call from the internet to the phone networks - a technology called "SIP trunking".

"Recently, because of the ease in implementing your own private enterprise telephone system, everybody can have access to critical telephone infrastructure," Mr Cirlig told the BBC.

"Because of this lower barrier of entry, it is very easy for scammers to build their own systems to spoof mobile numbers - the cybercriminals are essentially pretending to be legitimate corporate telephone networks in order to have access to legitimate telco infrastructure.".

He adds that right now, it is up to the VoIP provider to check whether the calls it is handing over to telecoms networks are actually legitimate.

"It's fundamentally the foreign VoIP providers that are technologically enabling these gangs to operate, so it will make a huge dent in this," he told the BBC.

Overall, the experts agree that the only way to completely fix the problem is to implement new telephone identification protocols that enable phone networks to authenticate that all calls and text messages actually come a real telephone number.

US authorities have ordered mobile operators to implement the protocols by the end of 2021, but Ofcom told the BBC in August that introducing full authentication in the UK will only be possible when the underlying technology that supports voice services is upgraded to become internet protocol-based (IP) networks, which is due to be completed by 2025.

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