What these guys said really.
You must be very careful if you pull the main fuse, and to be honest, if you are asking the question, im not sure you should do it. There are a number of things that should be done beforehand.
Older BS88 fuses do have a habit of falling apart when you try to remove them, especially if they havent been touched for a number of years, and this can be very dangerous. Its quite rare but very possible.
However, if you do decide to move it, they may well recommend that it is moved to an outside box, either surface mounted or recessed. They will fit an isolator if you ask. Some do it free and some charge for it.
You have to provide the box and install it and you have to dig and expose the cable for them to joint.
They also may not connect it unless they see a certificate for any works to show that the installation is safe.
Best thing to do is give them a call first before you do anything to see what they require.