The CM901 is a 24 hour timer. The CM907 is a 7-day timer, which has more flexibility, e.g. each day of the week can be individually set.
You would need a 3-core (plus earth) cable from the stat back to your wiring centre (junction box).
Thank you for your excellent advice. I will go down the Honeywell route now on your recommendation. My last question is that some of the replies suggested going wireless. The CM907 though is wired so the best/easiest I could do with that is get it into the hall. If I really need it in the lounge then than is about 60 feet away from the wiring center (and 3 rooms away) so in this situation wireless would be much easier. In this situation what model would you suggest. I like the idea of the 7 day programmable option.
Regards
Nick