The problem is still happening and now seems to have got worse after phone advice from VM. I didn't come back to you immediately as at that time service status line was saying that there was an area issue. During that time I got a period of 100% packet loss and no broadband for about three hours.
Once that went I again phoned VM yesterday and they got me to go through the normal checks (cables tight, reboot hub, factory reset etc.), then had me to reset channels on the hub. Initially it seemed to improve a little but now its worse than ever and the ThinkBroadband monitor seems to have even more latency. See the live link and graphic below.
What particularly annoyed me was that the guy initially tried to sell me an upgraded package 100->200mbs but as I had great broadband with the hub 3 and it only went wrong with the hub 4 . . .