Hi @Buka_sha
Welcome to the customers help customers Community of Vodafone.
In your device you turn on your roaming, which can be found on most devices under Settings and then Mobile network. There you have to see how you can turn roaming on or off. What it costs you depends on which subscription you have. For now, the UK is still in your data bundle. Data usage is deducted from your bundle. If you don't have a data bundle, or if you don't have enough, you can purchase a BloX, see this page. It is also useful to turn on BloX Limited Internet, if you then use too much data, you will go to a slower Internet and you will not incur any extra costs. Other rate information can be found here. And also read the Fair Use Policy before you go.
Have fun in the UK!