Money expert Martin Lewis has issued a warning to mobile phone customers over a 'dirty trick' being used to get more money out of you.

Speaking on the latest ITV1 episode of The Martin Lewis Money Show Live on Tuesday, January 20, Martin set out that the cheapest way to get a mobile phone contract is no longer to buy a phone outright and get a cheap SIM deal separately.

Now, Martin says, the cheapest method is often to go through a 'reseller site', which is not from the network directly but from a company which offers cheaper contract deals.

But, Martin warned, these same reseller sites often play a 'dirty trick' which is not illegal but is 'immoral', if you fail to cancel your contract when it ends.

He explained: "There is a dirty trick that mobile phone firms play, and it's from the resellers who I just recommended. They're the main ones who do this.

"If you go for a main network you'll normally get an airtime cost, so that's your tariff, and a handset cost that you pay for two years when you get a new handset from them.

"And then after two years if this is paid off, you just pay the airtime cost.

"What a lot of the resellers do, is they give you one price that includes the handset and the airtime and after two years when you've paid the handset off, you keep paying the same amount. So while you could be getting a SIM that's worth £6 to £7 a month, you're paying £30 a month.

"So those cheap reseller deals, note when your contract ends, draw a line in the sand and you need to get off it that day.

"That's exactly what happens here, it's why there are huge savings, you are still paying for that handset even though you've already paid the handset off.

"The problem is, it's not illegal. It may be immoral, in my view and that's a subjective opinion I give you lawyers, it may be immoral but it's not illegal so you're gonna struggle to get it reimbursed."

The Martin Lewis Money Show Live, Tuesday, January 20 episode is still available to watch via ITVX.