Responsibilty for electric cabling before the meter?

Tenancy Deposits

I had an electrician come in to do electrical safty checks. As a result he did a lot of work and I am now happy the place is safe.
Howevr, he has pointed out that there are two cables coming into my property. They both have 'the cutout' on them. One goes to my meter and one goes through a rusty pipe to next door.
He also pointed out that this other cable has a 6mm earth. He has replaced our earthing with 10mm as per current regulations and believes that the other supply should have 16mm earth as it is on the supply side of the meter.
There are such a lot of electric companies around who deal with the supply from the meter, but is there one company (like Transco for gas) who deals with electricity on the supply side of the meter.

It is clearly not right to have cable over your property that you are not are of and I want to write to 'them' to resolve the situation.

Aside form any other issue, should they be paying wayleave????

Thank you