Regulation on surface mounted cabling and wall penetrating cables for building entry call unit in a block of flats

regs wise there is nothing magical about interlock wiring. It should either follow a visible route (trunking, conduit and even surface clipped in areas of low risk are all examples of that) or if concealed under a wall surface, follow a vertical or horizontal line between fittings, or be deep enough (50mm say) not to be casually damaged by decorating or later building work work (shelves and notice boards). Or in the ceiling wall corner is considered a 'safe zone.
Drilling a hole through brick is fine, far better than damaging the frame, I'd expect the hole to be cleaned and mastic (normal or firestop depending on location ) to stop insects and draughts, a short length of plastic tube to protect it or guide it through a cavity wall may be appropriate, this is most important if the cable jacket is soft and may be scuffed. If the change of direction is too sharp then a box can be fitted on one or both sides of the hole.
Cables that are overhead, must be secured so as not to fall in a fire - so if there is plastic trunking stuck on a ceiling , you may need some builders band or metal clips that would stop hot sticky cable garotting someone trying to escape, and folk worry about plastic wall plugs, and like to avoid them if possible.
That's about it ;-) 
Mike
Edit https://uk-store.netceed.com/thick-wall-customer-lead-in-kit-061827-p10.html is an example of special thin conduit for protecting data cables, fibres and similar through walls

Hi Mike,

Thank you very much indeed for your quick response - all makes complete sense.

My basic public research mentioned only penetrating fire compartment walls (e.g. between Flats - Common Hallways) for necessary safety kit - fire alarms, emergency lighting etc.  If you do penetrate, use fire resistant cable and intumescent sealant.  So, should that ideally be steel trunking and boxes flanged over penetration points?

I did wonder whether the following 'guidance notes' might help me to point people at formal regs for fire prevention/control - to protect people from smoke/fire ingress into their flats/keeping common escape root clear, as well as protect the cables of course:

Guidance Note 4: Protection Against Fire is a vital guide to an important safety aspect of working with electricity.

Electrician's Guide to the Building Regulations includes the latest guidance relating to competent person schemes, third-party certification and covers relevant parts of the Building Regulations, including Fire Safety, Ventilation and Conservation of Energy.

I am not a practicing Electrician, so is it worth purchasing the above to dig into fire stopping guidance?

Thanks again for any thoughts.

Kind regards, Mark

Generally, unlike big drains or ventilation, the holes for alarm cables and so on are not significantly large  in terms of spread of fire ,and the use of intumescent mastic or stuffing is normally enough - the resistance to fire in hours is something to look at - trendy downlighters cut into ceilings are often problematic.

More generally the principles here https://www.gov.uk/government/publications/fire-safety-approved-document-b  are worth a look if not already perused. 

If you have a lot of cable in fire escape routes you, or rather your designers, may want to specify a low smoke and fume cable for those and other confined spaces, but to then put it in a PVC trunk makes little sense. Fire alarms are usually wired in FP series cables that carry on working long after normal ones have melted. Door buzzers and so on, generally not - unless there is a critical fire escape consideration but normally things can be opened from the inside even after the power has failed.
Mike.

PS edit to add links - expect to see something like this sealing holes

https://www.tlc-direct.co.uk/Products/FXFRCW.html
wires held up by these
fire clips
In a really big hole maybe 
https://www.fireprotectionshop.co.uk/product-subcategories/intumescent-pillows 
or if you want to see the options you usually don't need,
https://envirograf.com/product-category/electrical-and-plumbing/socket-and-conduit-protection/ 

Mike - this is very helpful - very much appreciated.  Your experience and pragmatic approach lands the important points very well.

I will read the Gov approved document.

Many thanks, Mark

Mike - this is very helpful - very much appreciated.  Your experience and pragmatic approach lands the important points very well.

I will read the Gov approved document.

Many thanks, Mark