Hi all,
Firstly thank you very much all for your helpful replies and help.
Since last Thursday, after resetting the hub for a 2nd time, and unplugging then re-plugging the white fibre box, it seems to have improved somewhat. Not full 900 but around 710mb. I've left it over the weekend and it appears to be keeping up so far.
Though it can still vary but seems a lot better. I'm going to leave it for a bit and see what happens, as I daren't touch it in case it has a relapse! If it resumes I will try some more of your suggestions such as skipping the hub and such.
In the mean time, thanks again chaps!
James