Had serious slow speed for a long time. But did not have time to sort anything out, stress in other parts of life. However 2 weeks ago, tried downloading a 550mB file and it took over 5 hours. So did a broadband speed test from moneysupermarket.com and I had a horrendous speed of 0.2mb/sec.
Searched online, disconnected everything on all sockets but router, and laptop, still slow. Could not do test on master socket, did not have a horizontal bar on my main socket. Then saw someone on another forum say router should be on all the time. Mine was not, I switched it on and off several times a day. Nowhere on the info guides said it needs to be on all the time. It seems that the every switch on/off made it think there was a fault on the line.
The openreach engineer came. He kept blaming my wire extension from my main socket to my socket into the bedroom etc even though they have been there forever. After moaning for several minutes, he changed the main socket to a more modern one, did a hard reset on the line and speed was 9mb/sec.
The engineer did not have a clue, he was trying to pass the buck, he did not listen, was impatient. Complete patronising **bleep**.
So if you have slow speed, it is worth checking that your hub is on all the time and getting a hard reset done on the line. The router was stuck at the slow speed until the line was reset.