Customers of major mobile networks including Three, Vodafone, EE and O2 have been warned by Martin Lewis that they could be overpaying – and now one network has responded with a promise.

Mobile firm GiffGaff has seen the 8 percent average mid-contract price hikes issued to customers in April and pledged not to do the same thing. It says it won’t increase prices midway through customers’ contracts.

Giffgaff currently offers unlimited minutes, data and texts for £35 a month – which equals £420 a year.

Alternatively, it has a £25 a month plan for 100GB of data and a super cheap £6 a month for 2GB.

Ash Schofield, CEO of giffgaff, said: “Most people don’t read small print and these unexpected mid-contract price rises are hitting during a cost of living crisis, when people need clarity and certainty of their monthly spend.”

“giffgaff is committed to no mid-contract price rises. We believe in giving people certainty on price and the freedom to flex their bills up and down each month to suit their budget. It’s one of the reasons we launched Good Contracts, to give people a better choice.”

Martin Lewis, on his self-titled The Martin Lewis Podcast for the BBC, heard from a caller who had managed to slash his mobile bill from £52 a month to just £9, a saving of over £500 per year.

This method only works if you’re not currently tied into a contract period (usually the first 12 or 24 months of your current deal), but Martin Lewis advises that there are as many as 20 million people out of contract right now who could save big.

To check if you’re out of contract, text INFO for no cost to 85075. Sometimes, just texting the numbe can lead to a better offer from your current network provider because they are legally obligated to send you the information and they know you’re shopping around.

Otherwise, you can use a price comparison website to find the cheapest deals.