Ofcom has proposed a set of new rules which would force mobile phone companies to tell customers when they are using potentially expensive texts, data and calls abroad.

The telecoms regulator said that while many mobile phone operators already do, it is planning to make it obligatory for them to text customers when they travel abroad.

According to research that it had commissioned, 19% of holidaymakers do not know they could be hit with extra charges if they use their phone abroad.

But 94% of travellers say they are aware of roaming alerts and 84% read them when they get them.

The study also found that 94% of those who read the alerts find them either essential or helpful and close to three quarters modify their behaviour as a result.

“Millions of UK holidaymakers head abroad every year and want to stay connected on their travels,” said Ofcom’s director of telecoms consumer protection Cristina Luna-Esteban.

“But without clear information from their provider, they could find themselves facing an unexpected bill for calling home or going online.

“These alerts would mean whichever mobile provider you’re with, you won’t be left in the dark about roaming charges and action you can take to manage your spending.”

The new proposals would force companies to tell customers when they start roaming, how much it will cost them and suggest how to limit the additional cost.

It also said that it hoped to take action on “inadvertent roaming” where you are still in the UK, but your phone connects to a phone mast in a different country.

This is a particular problem in Northern Ireland where 22% of customers reported that their phone strayed onto an Irish phone mast within the last year even when they remained north of the border.

But it even happens elsewhere. According to the regulator 2% of customers accidentally connect to French networks when on the English coast.