I did move the bookshelve out of the way last nigh and checked my speeds and this morning and there was no difference.
As I was about to go to bed I noticed that the green light on the front of my hib was flashing. I thought I would leave iy to see if this was still the case this morning and it was. I switched the hub off and the flashing ceased.
I think I should contact Virgin Media to ask them to reduce me to M50 or M100 (saving up to £10 a month) and I wonder if a wi-fi booster might help (£3 a month).