Thanks to all for your contributions some of which I want to expand upon - see below.

I found a useful summary of BS7671 requirements at:

• https://professional-electrician.com/technical/networking-data-cables-in-compliance-with-bs-7671-requirements-niceic/

My understanding is that Band 1 circuits (data comms, alarm, extra low voltage <50V ac, 120V DC) and band 2 circuits (220V AC lighting and power) must be separated. In the context of a domestic house, this seems to mean that they should not share the same conduit in walls/floors and that bundles of cables should not mix Band 1 and Band 2 cables and each should be separated in cable trunking (shelves) by 10cm, or put into separate compartments. Furthermore there should be protection against premature collapse in the event of a fire; a requirement that could be met by putting cable bundles located above false ceilings in metal trunking. There is also mention of the need to separate electrical cabling from non-electrical services like water pipes though close proximity is permitted if steps are taken to protect the wiring from damage, for example from a burst pipe.

In terms of the requirements for the cables themselves, it seems that they must be appropriately insulated; >220V for power/lighting and >50v ac for extra low voltage. However, the requirements for safety in case of fire do not seem to be specified in BS 7671, but instead are referenced in BS6701 (as mentioned by gkenyon).  I found a useful summary at:

• https://www.voltimum.co.uk/sites/www.voltimum.co.uk/files/fields/attachment_file/gb/others/S/200409135100BS6701BIP0007v1-001.pdf

It seems responsibilities for the installation of telecommunications equipment and telecommunications cabling are divided between the installer and the owner of the premises housing the telecommunications systems referred to hereinafter as the “premises owner”. A reasonable definition of 'premises' is a house or building, together with its land and outbuildings, occupied by a business. Therefore does BS6701 apply to a domestic house? Is there any case law on this issue? That issue apart, there is sense in me specifying cables that are BS EN 13501‑6 compliant - CPR Euroclass Cca,s1b,d2,a2

• https://www.nmcabling.co.uk/2019/05/do-i-have-to-install-a-euroclass-compliant-data-cabling-in-data-cabling-installation/
• https://cableintelligence.co.uk/blogs/blog/what-are-cpr-rated-cables

Summary

Clearly, it is not sensible to apply the same requirements for wiring systems in a factory or office block to the rewiring of my house. Even the requirements for a high-rise block of flats (Grenfell) are very different to those of a three story town house in single occupation like mine. It is unrealistic to expect home owners to spend many thousands of pounds employing consultants to obtain the documentation required by BS EN 13501-6 / 50174 in terms of specification, design, implementation and testing of a cable system that is just a single CAT5 cable running from the router in their basement to a network switch in their bedroom. Admittedly my proposed network is a little more complex, but the point is the same - some common sense is needed.

Given the increasing use of CAT5/6/7 cable in people's homes it would be useful for the IET to produce a guide on the subject. It should cover the minimum legal requirements to satisfy UK wiring regulations and also suggestions for best practice. In the absence of such a guide I am proposing without the intention to provide any form of professional guidance:

1. Specifying cable that complies with the legal UK minimum as specified by BS EN 13501‑6
   
   1. Euroclass Cca (reduced contribution to fire)
   2. Euroclass s1b (smoke production)- more stringent than low smoke, zero halogen (LSZH)
   3. Euroclass d2 (no flaming droplets)
   4. Euroclass a2 (acidity resistance)
2. Keeping data comms / alarm cable / extra low voltage cables (band 2) separate from three phase, 220V power and lighting (band 1). This means having separate cabinets (though some will need 220V power), separate wall/floor conduits and not mixing band 1 and band 2 in the same bundle so that they can be put into their own compartments in metal trunking fixed to walls above the false ceilings.
3. Keeping electrical cable separate from water pipes, etc. Ideally they should be put into separate compartments in the ducting between floors.
4. Using armored cable for three phase and any external underground power/lighting

I should be grateful for any further comments and suggestions on the above.

wpqs said:

that bundles of cables should not mix Band 1 and Band 2 cables and each should be separated in cable trunking (shelves) by 10cm, or put into separate compartments

BS 7671 says they may be run together if insulated for the highest voltage present. However, agree separation is better all-round.

BUT

BS 6701 currently requires at least 50 mm physical separation between indoor telecomms cables and power cables, even if metallic armour, screen or metal containment is used. (For some reason there is no such provision for outdoor cables.)

Of course broadgage 's recommendation of 10 cm meets this requirement.

wpqs said:

that bundles of cables should not mix Band 1 and Band 2 cables and each should be separated in cable trunking (shelves) by 10cm, or put into separate compartments

BS 7671 says they may be run together if insulated for the highest voltage present. However, agree separation is better all-round.

BUT

BS 6701 currently requires at least 50 mm physical separation between indoor telecomms cables and power cables, even if metallic armour, screen or metal containment is used. (For some reason there is no such provision for outdoor cables.)

Of course broadgage 's recommendation of 10 cm meets this requirement.

Does BS 6701 apply to a domestic house in single occupation? The preamble suggests it only applies to premises - i.e. a house or building, together with its land and outbuildings, occupied by a business