I use Asda Mobile (Vodafone) PAYG Sim Only, 30 day rolling contract so cancel or change any time.
And, it still gives free EU roaming unlike some.
Unlimited Minutes & Texts with 3Gb Data £5 a month, 5Gb £7, etc. 🙂
https://mobile.asda.com/bundles/pay-as-you-go
Please excuse spelling/typos. Apart from being a clot it turns out I had one on my cerebellum that's now causing various problems!