Subject says it all really. My Demon connection has become almost unusable for iplayer in the last month. speedtest.net generally gives 1.4mbit download speed at all times of day and night.
I have been a demon customer for 15 years and am now close to leaving as my router reports a 7616kbps downstream connection but I haven't ever seen that.
Best speedtest was 6mbit about 18 months ago, dropped to 3mbit a year ago and now 1.5 all the time (at least the last month or so).
I'm on homeoffice i think and should get "up to 8mbit" ...