My sincere apologies for the delay, I'm almost around the proverbial bend trying to get the info you want from my ISP, they may be the biggest in the UK but they also deserve their reputation as being the worst for support.
After 2 fruitless days all I've managed to gleen from them is that my line is working ok and the signal strength is good (should be I literally live 400 yards from the servers) The girl on the other end of the telephone line was obviously reading from a script because she was unable to help at all regarding line noise.
I have independently done some speed tests, the results are below:
As I have previously mentioned I have 2 desktops both linking to the same ISP through the same router. The one I use to do most of my work and with the most programs installled (pc A) is the one I am having the problems with, this is hard wired to the router. The second (pc B) has very few programs installed, is used mainly for research or cross checking, has absolutely no problems, and has a wireless connection to the router.
I have already confessed to not being particularly clever with the technical aspects of computers but I just cannot get my head round why one pc should be good for downloads and viewing videos and the other bad when they both share the same ISP and router connection to the ISP, unless there is something in pc A which is not present in pc B and which is causing a conflict of sorts, or the fact that the good pc has a wireless connection whilst the bad one is hard wired (I've checked the ethernet cable and this is ok).
Anyway the speed test results I got are as follows, hope they are of help, results are average of 3 tests on each browser on each pc. The only other thing I would mention is that Firefox always loaded up the test quickly whereas Chrome was sometimes a bit slower but IE always seemed to be slow.
on both computers the router was always showing as 18.4mb and the upload was virtually static at around 0.82mbps
on pc A (bad one) the download was around 0.15mbps but on pc B (good one) it was about 2.2mbps, one test even showed 3.68mbps.
Hope the above gives you food for thought and I would mention one other thing I have done since my last post. I read somewhere on the net that some people had experienced problems with IE8, and as I very seldom use IE I decided to uninstall this in the hope that it might just resolve my problem - regrettably it did not. By the way MS don't exactly make it easy to uninstall, took a lot of searching before I found their uninstall instructions.