https://www.moneysupermarket.com/mobile-phones/guides/roaming-charges-explained/
Nevertheless, there are still networks that offer inclusive EU roaming. Many budget networks – giffgaff, Tesco Mobile, Asda Mobile, iD Mobile, SMARTY, Lycamobile and Lebara – still include EU roaming for no extra charge in their plans. But there's usually a fair usage policy in place, which limits the amount of data you can use while you're away.
Nevertheless, there are still networks that offer inclusive EU roaming. Many budget networks – giffgaff, Tesco Mobile, Asda Mobile, iD Mobile, SMARTY, Lycamobile and Lebara – still include EU roaming for no extra charge in their plans. But there's usually a fair usage policy in place, which limits the amount of data you can use while you're away.