I can't say I have seen one of these. It resembles an electrical breaker circuit such as are used to switch of /on mains currents - it is not applicable to a Bt circuit - the bars may become corroded and for good measure it would appear they have proved earthing. It is best to run the incoming cable to a modern master socket. However it may be that this is not possible in your case as the incoming wires may not be suitably placed. I would suggest replacing this with a modern and cheap "joining box" I assume you have a master socket? - as this should be installed too. The best BB connection is by removing the Bt master sockets face plate and replacing it with a filtered master socket face plate such as the XTE-2005.
Does your Line come in via an overhead wire?
