Try a direct connection to the ONT as that will take the Hub out of the equation. See if speeds are stable there. The following is a rough guide as things may be slightly different between Windows versions but should get you going.
Thanks will have a bash at that in a few days
Hi, Finally got around to testing via ONT however still mixed results. The native speedtest app couldn't connect to internet but could through browser (417/89 at 1:49pm 483/106 at 1:50), as could google speed test (706/98), fast.com (390), broadband speedchecker (415/87).
The minimum speed guarantee is 700 but the only one that reached that was the google ST, and TBH it appears a bit of an outlier.
Tested again using original connection via powerline and that is now 58/64.
Using the BT speed checker from My BT app, after several attempts, they state speed to the hub 947 upload 111