Which doesn't stop sparkies doing it on new builds and signing it off as compliant.However the current regulations do not permit this ...
Mother was looking at buying a new build not long ago, she pulled out from it - but I was very tempted to get the sparky in who's signature was on the signoff, hand him a big nail and a hammer, and invite him to stick it in the wall where the meter tails were buried.
I would have thought that (from the supply industry PoV) the main reason is that a main fuse without a seal is scope for easy bypassing of the meter.I'm sure if the whole cutout and meter arrangement was to be designed from scratch today it would be quite different.
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It is not the damage done to the network which is the issue with 'yanking' the DNO fuse, it is the serious risk of injury to the person doing it or the long term fire risk if they don't carry it out properly.