The consumer group found that in some destinations holidaymakers could pay about £30 to upload a single photo while travelling outside the EU.

The consumer group is calling for trade deals to extend free mobile roaming beyond Europe.

It says that extending “Roam Like at Home” benefits would remove extra costs and inconvenience for thousands of Brits every year.

The cost of data abroad

The consumer champion analysed the cost of using data in the four non-EU countries that the UK government has prioritised for post-Brexit trade deals – the US, Japan, Australia and New Zealand.

It calculated the charges consumers face for simple functions such as uploading a photo and streaming a song, across 13 networks.

Which? found that British holidaymakers in Japan face having to pay sky-high charges when roaming there.

EE, O2 and Vodafone all have a daily cap of between £4.99 and £6 on charges when roaming in Japan. But Plusnet customers could face a £30 charge to upload a single 5MB photo.

BT, Tesco and Virgin Mobile customers could also have to pay £25 to upload a single photo while travelling in Japan.

Which? warned that customers who have adjusted their phone’s settings to automatically back-up photos onto the cloud could be hit unwittingly with these costly charges.

A Plusnet spokesperson said: “No-one likes surprises when it comes to their bills, so we cap roaming charges at £40 per month and allow customers to reduce this further if they want to. We also send customers a text when they reach 80% of their roaming cap and again when they exceed it, and these charges contribute to their monthly spend cap plan.”

Monthly caps

All mobile network providers have a 50 euro (about £45) monthly cap on roaming under current EU rules to prevent customers from racking up expensive bills.

But Which? research suggests customers could quickly hit their limit after uploading just one photo or streaming a few songs.

If customers request that their mobile network provider removes the cap, they could risk exorbitant roaming charges quickly adding up.

Trade deals

British holidaymakers have benefited from free roaming costs in the EU since “Roam like at home” rules were introduced in 2017. Unless an agreement is reached between the EU and UK, mobile operators could re-introduce data roaming charges.

A number of operators have said they have no current plans to charge extra, however Which? is urging the government to ensure consumers do not lose this benefit when the transition period ends.

Which? also says the UK has the opportunity to strike ambitious new trade deals that benefit consumers as it exits the EU.

It is calling for the government to include free mobile roaming in new trade deals it negotiates and as part of its future relationship with the EU.

Sue Davies, Which? head of consumer protection, says: “British holidaymakers can face exorbitant charges and see their phone blocked when roaming with some network providers in countries outside of the EU, with simple functions such as uploading a photo potentially costing £30 and streaming a song nearly £20.

“As trade talks intensify with priority countries, it is important that the government protects and ideally enhances consumer rights. Which? is calling for provisions to be included in these negotiations to put an end to some mobile operators charging excessively high fees when customers are abroad.”