Alterations can often be tricky. I guess the original relied on the DNO's fuses not only for isolation & overcurrent protection but for shock protection (ADS) as well. I guess the new cabling will be armoured (rather then all insulated) so will need proper co-ordination (earth fault loop impedance and fuse characteristics) to ensure safety. BS 7671 requires the DNO's consent for use of their fuses for overcurrent protection for consumer wiring - and these days DNOs either limit that consent (e.g. to around 3m of insulated & sheathed wiring of certain specification) or refuse it at all (throwing the consumer/BNO back onto BS 7671 rules for omission of overcurrent protection - which has a similar 3m limit). a BS 7671 certificate these days, will be issued under the current version of BS 7671 (and hence subject current DNO rules) rather than those prevailing 70 years ago or whenever. If the certificate is for the complete new circuit, it'll have to be based on the design, installation and inspection/testing complying with the current version of BS 7671. There may be some scope to claim that the work consists only of simple cable replacement, which might have some merit, but is likely to be undermined if a different type of cable is used (especially one that requires an earthed armour).

   - Andy.

Alterations can often be tricky. I guess the original relied on the DNO's fuses not only for isolation & overcurrent protection but for shock protection (ADS) as well. I guess the new cabling will be armoured (rather then all insulated) so will need proper co-ordination (earth fault loop impedance and fuse characteristics) to ensure safety. BS 7671 requires the DNO's consent for use of their fuses for overcurrent protection for consumer wiring - and these days DNOs either limit that consent (e.g. to around 3m of insulated & sheathed wiring of certain specification) or refuse it at all (throwing the consumer/BNO back onto BS 7671 rules for omission of overcurrent protection - which has a similar 3m limit). a BS 7671 certificate these days, will be issued under the current version of BS 7671 (and hence subject current DNO rules) rather than those prevailing 70 years ago or whenever. If the certificate is for the complete new circuit, it'll have to be based on the design, installation and inspection/testing complying with the current version of BS 7671. There may be some scope to claim that the work consists only of simple cable replacement, which might have some merit, but is likely to be undermined if a different type of cable is used (especially one that requires an earthed armour).

   - Andy.

Further to that there will be practical considerations to do with the space available etc. In some situations it is not possible let alone desirable to fit a switch fuse per flat on the area of wall you have. 

But is the Ryefield board the DNOs or the BNOs and does it have to stay that way? 

Well originally the former, as the whole BNO concept is far newer than most wiring,  but that is not the modern way, and the DNO may well be happy (even keen in some cases if it looks like it needs some work doing ) to relinquish responsibility for it.

If there are DNO  death or glory incomer fuses, one per phase,  and then one big isolator, the Ryefield board becomes part of the building network, and that can use it for then the protection for the submains - just as it always was.

Who has responsibility for the door key changes, but the wiring is more or less the same, but now it is the freeholder's problem to maintain.

Note the 'DNO bit' in this sketch from here, stops before the Ryfield.boad

.

Is this the sort of set up with a long submain to a 'red  link' secondary cut out next to a meter in each flat ? If so the original designers probably assumed that anyone working on the flat electrics would isolate there, and that having it hard to switch off the sub-mains would discourage casual mucking about with the pre-meter wiring.

There is also the question of if the main earthing and bonding is in each flat or in the basement if the supply is TNC-s (and a heck of a problem if it is TT, but I guess you would have mentioned that.)

Any installation, even one not to BS7671 can be tested and some results on a test certificate provided - but that may well not be enough - usually for new works, an installation certificate to the current version of BS7671  is required, and that does not have the same scope for notes about bits that do not quite meet the letter of the current rules.

Probably best if you can to clarify with someone what are the DNO happy to do and to connect to, and who has requested the work, and what exactly do they expect at the end of it.

Mike