Ping!

[#1]

We still don't know what's wrong
Are you connected wirelessly or with an ethernet cable to your router?  Which router are you using?
Have you done a tracert to bbc.co.uk yet?

[#2]

Can we go back to basics
Please post the stats from your router - speeds, noise margin, attenuation up and down
Post the full result from the BT speedtest
Post a tracert to 212.159.13.50

[#3]

can you post a link to BT speed test?

[#4]

http://217.35.209.142/ or http://speedtester.bt.com/