Hello, I live in the Wirral in a bungalow and have an issue with ingress from my neighbour who landscaped her property (of which the right hand side wall of my garage sits on her rear garden footpath). The builders who did the work breached my DPC and now everything we have heavy rain my garage floods. Her son claims its nothing to do with the work the builders did and it's the fault of my garage which he claims needs tanking out. I've had 3 drainage companies out who have all said that the landscaping on my neighbour's side is the cause of my flooding. What can I do to get my neighbour's son to accept this? 

We need photos of what has been done on the other side.

Any party wall agreement beforehand?

No there was no party wall agreement. I moved into my bungalow in February 2021 and my neighbour moved in later the same year. She had the work done the following year. The builders she used have ceased trading subsequently. The acodrain that you can see in the photo I've uploaded was uncapped so water was pouring into my garage. It has taken all these years to finally ingress.