Found some different firmware for my router, 4 year old firmaware, and have given it it a try. There seems to be some improvement, although it could be just because I reset the router.
After 3 weeks at a slightly better speed I lost connection (I think I put my mobile to close to the router when I was transfering pictures) and now it's back to -
The BT engineer visited today and basically told me I'd have to wait until the fault becomes constant they wouldn't be able to track it down and didn't know if I'd be charged for the visit as he is co ...
