Hi Andrew, Thanks for the quick reply.
I use the site you suggested plus
and the BT Openreach recommended site http://speedtest.btwholesale.com/
The results from any of these sites seem pretty consistent i.e. very good/poor or very bad!
The url here is one done a moment ago on the site you suggested. I can be reasonably certain that if I check it again in, say 2 hours, the speed will be about 65/68 meg.
As an aside, the upload speed varies very little, at any time.
As I say, there is not issue about specific times nor have I noticed any lag when I access any site - for example TBB/YouTube/Santander/BG/BT/eBay: all seem fine.
For the record, I live 300 or so yards from my street cab.
The url shows the IP profile - which the BT bod specifically said that if I can see that, then there is no problem on my line and it must be my PC.
Make of that what you will!
Again, any help or suggestions much appreciated