On Three UK's website, there's this note:
Go Roam update
To unlock your UK allowance in Go Roam in Europe, there’s a £2 daily roaming charge. When you Go Roam Around the World, it’s £5.* The daily roaming charge is triggered as soon as you use any of your plan's allowances in a Go Roam destination and lasts for 24 hours. If you’re on Pay As You Go, or your Pay Monthly plan started before 1 October 2021, these charges won’t apply.
I don't exactly understand what this means. Does that mean the roaming charge won't apply for Pay As You Go numbers period? Because that would make Three UK sims from Amazon a great option still.