The same is happening to me. Since last 5 days my download speed went from 11 Mbps to 1.5 Mbps (upload is just fine).
I have not changed hardware and have tried two different hubs (my own Netgear and the latest SmartHub) - well, this is ridicolous.
The technical helpdesk takes 30 minutes to pick a call on average and in one case a chap named "Vikram" disconnected me.
I've tried all the tests, and it clearly shows my download speed seems to be "capped" even if I pay the maximum tarif.
I live in central London, zone 1 - this is getting embarassing: I'm genuinely thinking about switching provider.
Ps. also the ping has gotten worse - from 5~10 msec to ~25 msec when reaching google uk... What a disappointment.
unless your post the information asked for no one here can help you resolve your problem
I'm glad I'm not suffering that much but do sympathise. The guys here really do try to help and have sorted my problems previously but on this occasion it looks as though I'm stuck with an unexplained 25% drop in speeds!
Best of luck