ah yes, sorry misread your post. The only one i'm aware of is EE on the iPad. It's more the embedded AppleSIM though. You can pay up-front for data on EE to use over a day, week or month without visiting the EE store for a SIM card. Nothing for the iPhone AFAIK.
not saying it isn't true, and I hope they do add this support ! (although I personally won't benefit being on an older iPhone 8), I am just wondering what the original source is for this information since it is not on news.o2.co.uk and they normally make posts for stuff like this. Only gizmodo are reporting it.
I have now moved over from EE to O2 . I had to port over to a physical O2 sim and then obtained a esim pack from O2 customer services which took 2 working days. The e-sim didnt work properly for the first day so had to reset network settings on iPhone 11 Pro and it is working perfectly. I also am now using O2 for my apple watch and that is working fine.
The whole eSim business has not really been implemented properly across multiple carriers in the uk. It’s way too painful at present to switch carriers or devices.