OK searching through this forum I find a number of threads about "pulling the main fuse" one of which is ongoing and about halfway down page 1 of this forum.
Despite the dangers it seems that some still think it is OK as they are consider themselves competent persons!
1/
It is NOT your property or the property of the building owner. Unless the owner of the main fuse has notified you in writing that you can withdraw and replace it you CANNOT.
2/
As it is their property they decide under the Electricity at Work Regulations who is competent to work on their equipment
(In reality in a DNO a competent person is NOT allowed to do anything on the live system, we have a number of levels of "Authorised Persons" above that)
3/
By withdrawing the fuse you may expose live terminals that are protected at s substation by large fuses (up to 630A). Show me where anyone (apart from trained DNO staff) is allowed to work in the vicinity of exposed live terminal.
4/
Yes it is rare for a prosecution unless something goes wrong, in that case the HSE will (and has) do the prosecuting.
5/
However DNO staff have, under the ESQCR Regs, the power to disconnect any installation they consider unsafe.
We would also do it if we think illegal abstraction has or may take place
(I have attended sites where electrical contractors have broken seals during rewires of "social" housing, tenants have subsequently stolen electricity)
Believe me I, for one, will not hesitate to disconnect if I find these situations, of course the Electrical Contractor might end up with some explaining to do to the customer if that happens!
(the last guy I disconnected on safety grounds illegally reconnected the supply, we then cut it outside. It cost him about £1000 to get it reconnected)
People have DIED by "competent" electricians making connections by cutting seals.
Do YOU want to be responsible for that!!
(DNO engineer trained and authorised to operate up to 33kV country wide)