Oh, I love good neighbour dispute!
Actually, they are just the worst sort of nightmare.
If you are a freeholder, surely there isn't a lease too?
Certainly not in Scotland.
If you own the ground, ie it's not communal, then no-one can put cables over it (except the statutory undertakings) without your consent. If it had been there for 10 or maybe 20 years, prescription might apply, so a wayleave established by usage which would not always show up in the title deeds. If you bought the property when the original cable was there, you may have a problem objecting now.ie objecting to there being a cable at all...however, if the new cable is substantially different from the old one, then you may have a case.
So, on electrical safety grounds, type of cable, height above ground, method of fixing/installation, you probably have grounds for asking for it to be removed or replaced in a better manner.
On legal grounds, if you own the property, the maxim ad caelo usque ad centrum would apply, and no-one has the right to obstruct your airspace.
Frankly, tell your neighbour to get a proper installation done, run it down the wall, bury it properly under the path, all at no expense to you, and if he wants a formal wayleave tell him to get his solicitor to draw it up and register it all at his expense.