The cap protected phone users from paying £130 for a 15-minute call, or over £65 for 50MB of data on some plans outside the most popular destinations.

However, data analysis by comparison switching service Uswitch reveals that, in total, Brits have had to shell out £539m in unexpected roaming charges over the last year.

Roaming costs are inconsistent across plans and geographical areas. Sky Mobile, giffgaff, O2 and Three have kept the voluntary cap in place, while Tesco Mobile scrapped it.

Networks typically only include data in the cap so calls and texts are charged, but giffgaff confirmed it includes calls in its roaming plans.

Sky Mobile customers visiting the Maldives or Seychelles will be charged £8.64 every minute for calls to local or UK mobiles and landline numbers. A 15-minute call will cost £130. Bolt-on services to extend UK allowances abroad are often limited to the most popular destinations.

Some providers will prompt users to purchase data add-ons on arrival, but prices are high. EE charges £65.32 for 50MB in Costa Rica, Ghana, Vietnam and some other destinations.

Roam-like-home monthly bundles can be purchased from providers, but offer varying rates and cover different countries.

iD Mobile Roam Like at Home offers free usage in 50 worldwide destinations and BT Roam Like at Home charges nothing for 47 destinations. To cover 83 countries, Vodaphone Rest of The World charges £6.85. All are subject to a fair usage policy.

However, there are ways in which you can reduce your roaming bills.

Six tips to reduce roaming bills

1. Download maps, films, and music while in the UK. An hour of Google Maps equates to 5MB. Streaming an HD movie for an hour uses 2GB.
2. Arrange a personalised spending cap with providers to avoid surprise bills and confirm limits to avoid unexpected charges.
3. Some providers charge for voicemail. Arrange to deactivate this before traveling.
4. Enable Wi-Fi calling or download apps such as Whatsapp to make audio calls and avoid using minutes. Ensure access points are secure before using public Wifi.
5. Utilise flight mode to avoid charges while in transit across different countries.
6. Consider a no-contract one-month SIM only deal to eliminate unexpected costs while abroad. For £4.96, Lebara offers a 5GB monthly SIM with free roaming in the EU and India

‘Be wary of shock costs’

Rehan Ali, Uswitch mobile expert said: “Anyone travelling abroad from the UK should be wary of potential shock costs, even if they think roaming is included in their tariff. These costs can sometimes be incredibly expensive, so it’s vital that customers research ahead of their trip and put measures in place to avoid a sky-high bill.”

“The safest option is to manually apply a monthly spending cap before travelling for each account that will be used abroad. This is particularly important for children and teenagers with access to a phone, as one in 10 parents say their kids have been responsible for an unexpected roaming bill.”

“Given how confusing these policies and plans can be, the key piece of advice for anyone looking to enjoy some time abroad this summer is to thoroughly research your plan ahead of time and speak to your provider to avoid any nasty shocks.”