As for the comment regarding the fuse size, I replaced like with like (the casing states a 100A fuse).
The casing states the MAXIMUM size fuse the cut-out is rated to carry, NOT the fuse size that was fitted!!!
To reiterate earlier comments
It is NOT your property and you had no rights to start interfering with it
Folk (even trained folk) have been seriously injured or killed working on these devices (rare but it does happen)
If it was disconnected for revenue protection you have committed an offence that gives the supplier/DNO the right to disconnect the supply external to the property. Cost of this and re-instating it could be in the region of 4 figures - for which you (or the estate) are liable.
If it was disconnected on safety grounds you may have inadvertently introduced a serious hazard! Safety grounds could include that it is in disrepair so could be subject to vandalism or illegal entry, you need to ensure that the property is secure at all times and is regularly checked.