Many thanks to all for responding.
The mixed response reflects the searches I carried out previously. To my mind the suggestion that Fruit Bat /\0/\ makes should work - logically - as the digibox is being used only for analogue VCR/DVD (or maybe both) and would be separate from the TV which has its own digital tuner. I understand the point Woodchip is making but think this would be the case if the TV tuner was being used to support the analogue equipment as it can't do two jobs at once.
It would have been helpful to many if Digit-Al had provided more information with regard to peripheral equipment instead of concentrating solely on analogue TVs.
If anyone has tried to do what I wish to do I would really appreciate their results. In the absence of such information, it looks as if I shall need to find a compatible digibox and experiment myself.