Shy - the reason they asked you to that was to enable the router to be plugged into the test point in the main socket. A speedtest there will eliminate any problems caused by faulty extension wiring. ISPs will usually ask for that to be done before they escalate the problem to BT for a line check (which the ISP has to pay for).
I was aware of the reason, having spent many hours trying to get Sky to escalate the technical advice to someone who actually knew what they were talking about, rather than repeatedly going through the same hoops dealing with a numpty reading from a checklist and getting absolutely nowhere! I'd already done extensive troubleshooting myself and had ruled out that there was any difference. The problem appeared to have been the distance from the exchange to our village and the number of subscribers sharing the over-worked network in my area. The speed was just about usable in the early hours but for much of the day the speed became so slow, or often non-existent, that pages constantly timed out before loading. Speedtest wouldn't often load all day.
Thankfully, the BT service, using the same socket, but more modern fibre optic equipment their end, was instantly far better and I now get 37-39 Mbps download and 8 Mbps upload. I wouldn't go back to Sky even if it were free, because it became unusable. Judging by the high number of BT Wifi hotspots around here, many others have taken the same step.
