I had that earlier today when I did a speed test, but mine was doing an IPv6 Speed Test, speedtest.net was fine with no issues, so I waited an hour or two and retried the TBB speed test and it was back to normal.
There is no point me doing a speed test atm due to congestion where I loose half my connection, but its still better than what I had on ADSL
Paul
BTBroadband - Infinity 4 - 310Mbps (down), 31Mbps (up)
TBB Speedtest