Money expert Martin Lewis has issued an urgent message to Three customers as well as the two networks which piggyback off signal.

This week, took to Twitter to urge customers of 21 banks to use a three-digit code to avoid getting scammed.

He revealed in a video he posted to his account that customers of most major banks in the UK can dial a three digit number to check whether the call they're having with their bank is actually legitimate and not a scam.

The founder said: "If you get a call from your bank, you're not sure it's really them, they're asking for personal details, you're a little bit worried. Just say 'I'm going to call you back via your switchboard, (hang up) and dial 159.

"This is done as an anti-scam and anti-fraud initiative so that you can always get through to a legitimate number without having to look it up. Just remember 159."

The three digit scambuster number currently works with 21 banks and building societies, including Barclays, HSBC, Lloyds, , , Revolut and as well as Bank of Scotland.

It works because 159 can't be spoofed or impersonated so scammers can't use it to trick you into thinking you're talking to your bank.

But, Martin has now revealed that Three customers as well as those on networks which use signal have reported problems with the number.

He returned to Twitter with an urgent update for Three customers, as well as those on Smarty and iD Mobile, which both use Three's signal.

He said: "We've worked out why some saying it doesn't work...

"Three has confirmed there is an issue impacting 159 calls made from some Android devices via its network (including Smarty and iD Mobile). It says it is working to resolve the issue as soon as possible."