Thanks I'll give that a go.
Is this not similar to the engineer who came out and looked and said I was already using a filter?
I'm afraid I don't know what G.INP means.
the master socket you currently have is already filtered but some posts have had problems with front not sitting correctly so using a filter in test socket and then connecting hub will maybe help. after you connect filter and hub then check the hub stats to see if speed any better including attainable speed
https://www.increasebroadbandspeed.co.uk/g.inp