Are you in a VOD enabled area?
If so ntl have a tool which can check exactly what was watched (what time it was ordered, how long it was watched for etc etc).
Do you have more than one Set Top Box, or just one? Also do you have any teenage children who can have guessed the pin number? If you didn't change it yourself, then the it is likely to be the default of 0000.... horny teenages with internet access could probably find that out
---------- Post added at 21:19 ---------- Previous post was at 21:06 ----------
oops didn't read that very carefully... VOD isn't analogue is it
not sure how it works for Analogue, but ntl should have a system for checking what was ordered and when... Second half of the above post still applies though!!