As of today, (15th June 2017) data roaming charges for all travellers in the European Union have been abolished, as part of the wider project to create a Digital Single Market. The European Commission has produced a couple of useful factsheets (see links at bottom of article) on what this entails. However, as this BBC article explains, customers are still liable for extra charges if they exceed their contractually agreed data usage limits.
As the BBC article also points out, once article 50 has been fully implemented, it will be the up to a future UK Government to decide as to whether the UK adopts these pricing restrictions or not.
As the last step towards the end of roaming charges by 15 June 2017, representatives of the European Parliament, the Council and the Commission have agreed on how to set the prices operators charge each other when their customers use other networks when roaming in the EU.
3.2 cents per minute of voice call, as of 15 June 2017
1 cent per SMS, as of 15 June 2017
They also agreed to a step-by-step reduction over five years for data caps, decreasing from €7.70 per GB (as of 15 June 2017) to €6 per GB (as of 1 January 2018), €4.50 per GB (as of 1 January 2019), €3.50 per GB (as of 1 January 2020), €3 per GB (as of 1 January 2021) and €2.50 per GB (as of 1 January 2022). The agreement is the final step to making “roam-like-at-home” work as of 15 June 2017, as foreseen in the Telecom Single Market (TSM) Regulation. It means that when travelling in the EU, consumers will be able to call, send SMS or surf on their mobile at the same price they pay at home. More information is available on the Commission’s Roaming website.