I’m in S Wales, see ya in half an hour 😂
Electricians can request permission to remove the cut-out fuse, enabling them to carry out work on the consumers side. Some DNO’s turn a blind eye, as it saves them the hassle of comming out for a 10 minute job and will pop round when its convenient, whils’t others will allow electricians to crimp on new seals. For example Western Power authorised me company to recrimp after removal and this has carried over since they became the National Grid.
Energy supplier’s are naturally authorised to carry out this work.
As said, I see to failures here (1) Octopus or their contractor, should have installed an isolator at the time of smart meter installation and I would certainly be ringing them and asking why one wasn’t installed. (2) Your Solar/battery installers, should have picked this up at the survey stage, giving you time to have sorted something out from Octopus or your DNO, enabling a local sparky to have done the work for a fraction of the price you have got to pay. I would question the company fitting your solar/battery, asking why this wasn’t picked up during the survey, as its put you out of pocket on what you thought was an all inclusive price. Certainly worth bringing up!