It could be radiating interference. What about the question regarding powerline adapters?
They aren't connected. Oddly at the same moment I disconnected the TV from the satalite, my son tells me the online game he was playing hung..
That sounds ominous. Leave it disconnected, and check the connection speed on the home hub now.
As you only got 40/20 from Sky, it could be that your line quality has always been poor. You could have an unbalanced pair, or aluminium cable.
The problem is going to be that you are getting above the minimum connection speed, so Openreach would probably not be interested in looking at it.
Not really sure there is anything you can do at this point, apart from wait to see if it gets any better.
That cannot be right @Keith_Beddoe as OP says he had 70+mb connection speed on infinity before he left for sky 2 years ago suppose maybe different pair and more crosstalk