If the UK leaves the EU with no deal all of the above will end as the UK will not be in the digital single market. “This might affect the amount of calls that you can make, texts you can send and data you can consume, including applying limits that are less than the amount available in your bundle when you’re in the UK.” The advice from the UK Government is to contact your mobile operator to see what deals they are offering.
https://theorkneynews.scot/2018/10/31/how-to-prepare-if-the-uk-leaves-the-eu-with-no-deal-using-mobile-devices/