Simply you can't.
Either you ask for an isolator
Or you have supply disconnected and then reconnected which is likely to be days rather than hours apart.
Or you provide a new consumer unit and tails and ask them to transfer power.
Because of the rules and regulations they are not permitted to give you permission to draw fuse. I know many electricians do but they are breaking the regulations by doing so. Normally if the house holder then tells the supply authority the seal has been broken they will come and re-seal with out too much hassle but that is up to the discretion of the supply authority and they can start proceedings and or remove supply.