Slow speeds and disconnects - anything more I can do ?

[#1]

For a few months I've been having odd periods of very slow speeds. It's now getting much worse. I usually synch up at 4M or so but on average at least once a day it resynchs often as low as 160K and sometimes I get complete disconnects. Of course the 160K synchs reduce my speed cap to 135K so even when the connection speed goes back to normal the capped download speeds are rotten.
I've tried just about everything mentioned (run speedtester a few times, changed filters, changed modem/router, upgraded router firmware, disconnected everything except modem etc). The only thing I can't do easily is connect directly to the BT main socket cus that's in a small entrance hall about a foot from the front door but I have tried several different cables between that and the modem/router.
Is there anything else I can try or is it time to raise a fault ?
Steve

[#2]

Hi Steve,
Are you able to connect your router to the master socket and then connect your router to your computer using a longer piece of ethernet cable?  If you're still having problems after that then I'd definitely advise raising a fault and getting a BT Engineer sorted.

[#3]

Have you listened to your phone line (POTS) to make sure you haven't got any crackling or other occasional or consistent noise? Unplug everything else to check and do so with a good corded (not cordless) phone.
If so, report a telephone fault to your landline provider (don't mention the broadband).
If the noise is intermittent, report it when it's crackling so they can hear it at the other end and ask them to log the fact that it's intermittent.
Regards.

[#4]

Had huge problems for quite a while too, turned out to be my old fridge which caused interference on the line which would cause disconnects and throttle back the speed. Would agree with above post  i.e. disconnect house electrical items one by one to pinpoint the fault.Good luck.

[#5]

Hadn't implicity included the electrical items :-[, but yes I would have subconciously done them as well. Fluorescent lights can sometimes cause big problems along with boiler startups etc.