1/ Do I have to maintain any physical separation between the main wiring
and the low voltage network wiring.

Basically yes.

LV mains cabling (i.e. standard 230V stuff) must be separated from extra low
voltage comms cabling by either:

(a) 5cm
(b) Physical barrier
(c) Comms cable with mains quality insulation/sheathing

(b) is the usual method, especially if your trunking has a separate
compartment for it.

(c) is normally impossible to find for data cabling, although you can use
multicore mains cable for some applications, such as intruder alarms, to
avoid the need to separate physically.

Christian.