It all depends on where you'll be using it.
Try this form and input the country you'll be in and input UK as the country you'll be calling:
https://www.tescomobile.com/roaming
I just used it and used Spain as an example. It tells you how much it will cost if you go over your allowance, plus it also states (for Spain):
//// For all of 2023, with Home From Home you can use your phone in our 48 European Home From Home destinations just like you do at home. You can use your minutes, texts and data as normal, and if you run out, you just pay our standard rates below, as you would at home. For pay as you go rates. ////