As you say your normal speeds are fine for your ip profile, do you know how to log in to your router?
because this could be a dns issue, i use opendns and there are different servers i am routed to on the bbc's services than if i use my isp's dns servers, (BT).
If you know how to fiddle around with your router change both your dns servers to
the reason for the dns change is that many isp's try to serve external content from within their own network to save on data charges accross external pipe's.
if you dont know how to login to your router say so and i will guide you.
Let us know how you get on.
Hope to hear back soon.