I know what you mean, I'm in Stockport too and t'internet has been a bit erratic here. Same happened about a month ago when I phoned CS/TS whoever, and the nice lady asked me more or less straight away to download the test file and see what it was coming in at. Alas it was only about 120, a mere tenth of the expected speed. She said ok unplug the cable from the router and plug it into the net socked and see what happens, to my surprise it was now coming in at 1,200.
The moral of my experience is that every so often, and increasingly more often I have to reboot the router and all is well.
It looks like soon I will have to buy a new one