yes consult the DNO. It is their Earth not yours. It’s their TX not yours. It is their engineers that calculate where and when a neutral can be used as CNE.
No if you ask them for permission and they say ‘yes’ then you can. Obviously.
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With TT systems, the consumer must provide his or her own connection to Earth, i.e. by installing a suitable earth electrode local to the installation. The circumstances in which a distributor will not provide a means of earthing for the consumer are usually where the distributor cannot guarantee the earth connection back to the source, (IET)
IET. Guidance Note 5: Protection Against Electric Shock, 7th Edition.
That means you are guaranteeing it! But it’s not yours! ESQCR 24 you will be in jail.
installations supplied from TN-C-S (PME) systems, in view of the risk of danger in the event of an open circuit neutral fault on the distributor's low voltage network. ESQCR Regulation 25(2) prevents a distributor from providing a PME supply to premises (IET)
IET. Guidance Note 5: Protection Against Electric Shock, 7th Edition.
ESQCR 25 (2). Taking a DNO supply and provided earthing arrangement out of their specified equipotential zone. Jail.
You do understand that out of all the documents electricians ‘use’ BS7671 is the last one! And it starts with EAWR 89 and ends with ESQCR....with HASAWA and CDM regulations in between...