Thanks for the reply.
It seems to have been a "one off". The stats show that I between 08:00 and 09:00 on the 13th of June I downloaded/uploaded 68.904GB/1.384GB, an impossibility given my line speeds (plus the fact that I haven't heard from BT to say that I've exceeded my 10GB allowance
). The figures have been more normal looking since that time.
If I run a "calibrate" from the "Test" menu, I get the following message every time:
The calibrated data correction is outside the normal range, if your speeds subsequent to this message look wrong or suspect. Disable calibration via Test Tools / Reset Data Calibration or run the calibration again.
Doing a reset makes no difference.
The calibration taskbar pop-up shows the correct download line speed of around 2900Kbps but the tbbmeter graph seems to show twice that value (the Kaspersky problem?). I have a spare Norton Internet Security licence, I'll try uninstalling Kaspersky and installing Norton instead to see if that fixes the problem.