Neighbour being a bit unreasonable?

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Neighbour has some issues with drainage / surface water on his property.
It hasn't been helped by the local road dumping water into his property when there is heavy rain....
He has been on at the council / mp's and everyone he can think of to try and rectify the situation, but with no luck.
I arrive home to see a hole drilled in the wall which separates the gardens of our houses. Probably about 10cm in diameter...
When confronted about it he says he had no other choice, as he has tried everything else!

Within a few hours the area around the hole is now a puddle, with every other area around my house bone dry...
So it looks like his solution was to dump the excess water into my garden!

Anyone ever had any experiences with anything like this?
I have sent an email to my solicitor for advice and will likely go see the cab as well, but was hoping someone on here might have a similar experience.

 

[Showboat]

His house sits about a foot above mine. So he has drilled from his lowest level diagonally downwards. I'm worried that properly sealing it will be difficult. As any water that gets into the wall will seap through and get into my garden regardless.
My wife won't let me speak to him as I know myself I will loose the plot!
I think it's a shared wall.
I like the criminal damage idea!!

 

[Showboat]

Thanks for the replies guys!
Maybe 10cm was an exaggeration, but I could certainly get my fist into it.
After the heavy rain at the weekend, my garage floor is now wet all over.

I don't see this causing any flooding to his house, more a build up of surface water in his driveway.
It's been an ongoing issue for him for years, so why he choose to do it without any warning to use is a concern.

I'll hopefully get a reply from the solicitor today. Maybe he did it because i am trying to sell the house and he knows i won't want any legal hassles / disputes.