I'm in the same boat; I've just swapped from sky (flawless service for 4 years, I add) to find my infinity service drops to near ADSL speeds at peak times. It's completely unusable! During the day it's absolustely fine so its clearly a severe congestion issue within BT's infrastructure.
Have you spoken with our technical department for help? They will have asked you to perform speed tests during the times you're reporting a slow throughput. You need to use one wired connection for the test. The site is http://speedtest.btwholesale.com. Once it's complete perform further diagnostics to send the results back to our suppliers servers.
How long does that take and how can we escalate the problem faster? I assumed they have tools to monitor congestion at each exchange and scale the network accordingly?
This is what I observed friday night
This what i get during the day (test saturday morning)
bt exchange bt line bt cabinet sky use the same as bt so why slow speeds with bt but not sky wouldnt you have network congestion with sky ..having same problems and have been for 3 mths total joke if you rise fault bt just close it fix or not makes it look like they are fixing faults when they are not.