Infinity Web Loading

I'm on BT Infinity option 2 and over the last few days web pages have been starting to load slowly and even occasionally dropping altogether. I've carried out a few speed tests and they seem fine as well as downloading and that too is fine. Ping times seem fine too.

I switched to Google DNS but that hasn't seemed to help much. I've also tried in IE, Firefox and Chrome and the problem seems to exist in all 3.

Is there anything else I can try to track down the source of this problem?