Money expert Martin Lewis is urging people to send a three-letter text in order to slash their bills instantly.

The founder of Money Saving Expert returned to his podcast - The Martin Lewis Podcast - on BBC Sounds, Spotify and Apple Music this week with another top fiscal tip, this time for anyone with a mobile phone out of contract.

You can now get 150GB of data per month for 'a little over a fiver', Martin told his listeners, and there are as many as 14 million people who are out of contract right now and free to switch. First of all, step one is find out if you're free to switch. Text INFO to 85075 - this will tell you if you're in contract or out of contract and how much it will cost to switch. With Three, Smarty or ID Mobile you also need to reply with your date of birth.

Second, find the best deals by doing a price comparison 'by finding the cheapest SIM that fits your needs', says Martin. Generally, the best deals come from price comparison websites with promotional deals on top of the tariffs.

Step three is find a virtual network and find a cheaper price on the same signal. This is because many mobile firms actually piggyback off a larger network. There are only four real networks, and two of them have just merged. Vodafone, Three, O2 and EE. Every other network just piggybacks off the big four's signals. But fims like Smarty (uses Three) and Tesco Mobile (uses O2) are the same signal and network, just at a cheaper price.

But you can skip the first three steps in many cases and just use ask for your PAC code with a three letter text: PAC.

Martin added: "There are four steps to slashing your mobile phone costs, and right now SIMs are dirt cheap. So if you're out of contract, it's worth doing.

"But what's interesting is the final step, which sounds like it's a technical step, but does have a hidden bit of money saving magic.

"The last step in the process once you know where you want to shift your mobile phone custom to is to text PAC to 65075. It's free. What that does is request your porting authorisation code from your existing mobile phone provider, that you can give to the new one, so you can move your number across.

"But often when you do this, if you're out of contract, your existing provider will say, please don't go and will often include in that an offer to keep you. It's virtually a way of haggling, so sometimes people go 'oh I won't bother they're now offering £20 a month off'.

"So if you're very cheeky, and while I prefer you do all four steps, if you're out of contract, just text PAC to 65075, pretend that you're leaving and see if they offer you a better deal to stay. Let me know how it goes."

The latest June 19 episode of The Martin Lewis Podcast is out now on BBC Sounds, Spotify and Apple Music.