I'm no expert, and have only just signed up myself, so I will defer you to MSE.
These 2 companies are competing, so if you're really keen/skint, you can signup for 6 months then swap (porting over your number).
1) LEBARA [uses Vodaphone]
2) LYCA [uses O2]
The former gets better reviews. Cancel anytime.
🛒 Amazon Deals (Assocs earn a few pennies) // affiliate sign-ups: 🎧 Audible / 💰 TopCashBack / 💵 Bing Rewards / 🔐 NordVPN / 🌐 Hosting
