I don't think that download speed will be classified as suffering congestion and is nowhere near the very poor 2mb in your initial post
No, it's nowhere near as bad as the 2Mbps (which should have been logged on the BT Wholesale server). I'll post another snapshot next time it plungs that low!
So, how poor does my download speed have to be for it to be considered that there's a throughput/congestion issue? Is 66% of my sync speed with a 122ms ping considered perfectly acceptable? And is never seeing >80% of my sync speed also considered acceptable?