Weird setup

[EFLImpudence]

I would suggest it depends on what "clamp off the existing earth connection from the main supply" means.

 

[AndyPRK]

Take the earth to next door?

 

[securespark]

That's not a valid solution, and having the fuse for your neighbours property on your side isn't good either.

It could well be that the "fuse" is a link and the actual fuse is on the other side of the wall.

 

[securespark]

Does that look like the right type of clamp for the earth - or just a DIY job with the wrong clamp ?

It used to be common (if bodgy) fix by DNOs, at least here in the NW. Nowadays it is frowned upon.

 

[securespark]

Oops....