Hi there.
It's not clear what connections you have so my reply may be more confusing than helpful. I have an ntl box running through a Sony DVD recorder and it works fine. I have the connection from the wall going to the ntl box, then a scart cable from the "tv" connection going to the AV-in connection on the Sony DVD recorder, and finally a scart from the Sony to the TV.
If I am recording a digital signal from the ntl box it's on Line 1 on my recorder (selected using the "input select" button) and it records whatever channel is selected on the ntl box. (Obviously I cannot watch another digital channel then.)
If I want to watch regular analogue signals when recording a digital signal I simply selet the channel on the tv.
Don't know if this helps at all? If I can be more specific let me know what connections you have and what model recorder you are using, then maybe I or someone on here can help you out.
Good luck. You will get this sorted.