@NVP Ah man, so higher is better, dammit
I've been with BT for 6 years using powerline adapters, 1 year with Vodafone using them in my current house, neither caused me any problems. I think maybe it was a dodgy smarthub rather than a general BT issue.
Most probably, but I seem to remember finding a few other people with similar issues. I'm not sure how it was caused, but it had me tearing my hair out for a good while. I was back and forth with Plusnet because I was convinced it was a general connection issue. Then I realised the problem only occurred when I used my PC, connected via a powerline adapter...wireless devices, and the devices connected directly to the router were fine. I borrowed a 30m CAT5 from work for a few days and ran it up the stairs to the PC...and the problem immediately went away.
I had this problem both with a BT Smart Hub and a Plusnet Hub One...think these are very similar internally. Not sure why but they just hated my powerline plugs...they weren't, particularly cheap or anything though (TP Link IIRC). Never really got to the bottom of what the actual fault was...I can only think it was some sort of interference, but it actually caused the router to lose broadband connection entirely.
Just to say, I also tried buying different powerline adapters as well, but had the same issue. I didn't fancy trying to buy an aftermarket router to eliminate that (having already tried 2, albeit similar ones), which is why I ditched the powerline and ran a cable. Which was annoying becuase powerline adapters are really quite an elegant solution.