Understood but I think 300 MB/s homeworks is only available as an extra option when area upgrades have taken place.
Likewise the checker on
www.virginmediabusiness.com will only offer 200 Mb/s maximum until an area upgrade takes place, then it offers 300 Mb/s.
The discrepancy I see is that
https://keepup.virginmedia.com/speedupgrade says the upgrade has happened, but the services it should then make available are not.