BT say it's now fixed:

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Time resolved: Sat 13/12/2014 at 08:22

We were aware of an issue, which was causing some customers to experience intermittent issues when attempting to load web pages.

We have fixed the problem and apologise for any inconvenience caused

I'm not convinced that they've fixed it yet. Been having lots of pages time out, pages load without images, etc.

same here,had a few issues this morning

I'm still having problems, slow loading of pages, sometimes not loading at all. I'm on Infinity 1 and it's an intermittent problem that's been going on since December but I blamed it on a slow computer until I tried another.
It's not browser related as I use IE8, Firefox and Chrome. Chrome is slowest as I use an encrypted connection but IE8 seems to be the most likely to be so slow it times out sometimes. I'm sure it isn't browser-related though.

I've noticed it slowing down again the last day or two.

I can't help wondering if the original problem was related to some sort of packet inspection kit not being able to cope with the load which was resolved by taking traffic away from it. I'm now wondering if BT are gradually re-introducing traffic and waiting until people start complaining again.

John.