From the photo, the box in the middle appears to be some sort of electricity board junction box. The supply from the distribution system comes in from the white pipe below. This centre box has a lead seal on it, which is a sign it is something to do with the electicity company. The two grey wires emerging from the top then pass down into the bottom of your meter on the LHS. The two grey wires emerging from the meter then pass under the centre mysterious box and into your consumer unit on the right hand side. The mystery box is therefore on the electricity company side of your meter, is definitely the responsibility of the electricity company and cannot impact your meter readings. The cable emerging from the centre box on the rhs is a clue in that it looks like a supply to another part of the dwelling (via another meter).
I suspect that you have a shared 100A cable supplying both you and other parts of the dwelling. This centre box is an electricity board 100A fuse, protecting the 100A rating on the supply cable. If both you and your neighbours draw a heavy current (both have electric cookers on, say) the central fuse is likely to blow.
The solution is to have your own supply cable from th 440V three-phase distribution point (probably in the road) but the supply company will want money for doing that.
Do you live in a large house split into flats, perhaps?