Tonight I managed to get Oreo to pop up on my UK spec Nokia 8. I will go through my particular use-case and people might be able to replicate it. It *might* be that Oreo is already rolling out and that this is just a massive coincidence but I present to you all what I did anyway. It is currently downloading so I can't give any feedback on the actual update.
A few days ago I factory reset and set up the phone afresh, albeit without a SIM. I was previously using an EE SIM.
I have been checking for updates every few hours for the past week. I used Nord VPN to connect to a Finnish server last week but it didn't do anything.
This evening I checked for an update once more, with the usual disappointing result. I decided to try NordVPN again as I hadn't used it since resetting and setting up without a SIM installed.
Checked for update
Usual 'up to date' message briefly flashed up, then lo and behold the Oreo update download option appeared!
Thought this might help someone out there. Failing that, the update is already rolling out and it's just a massive coincidence on my part. I don't know of anyone else with a UK spec Nokia 8 who's had the update yet though.