Posted: 30/01/2017 at 17:50
The promised update in case it may be of help to anyone in the future.
As some pointed out on this thread, it constitutes a "Private Nuisance" as opposed to an illegality.
Having spoken to my local council, I am assured that it is not something they are able to deal with nor do they advise taking private action unless I can categorically prove the discharge is damaging my property or interfering with my enjoyment of the garden.
With regard to Building Regs, I am informed that provided the regs were followed when the property was constructed , in this case a flat roof extension to an old building, the property owner can alter his drainage as he sees fit. Whilst it is reccommended that surface water be discharged into mains drains or a soakaway, it would seem that one is not obliged by law to do so. The fact that my neighbour is running his downpipe along his wall ( within his own property as such ) makes it all the more difficult.
Since I last posted, the neighbour has partially turned the "elbow" so that the rainwater discharges on to the top of the wall rather than blatantly discharging down into my garden. The wall has obviously suffered from water corrosion over the years this has been in place but either he can't grasp this or doesn't want to.
Much as I did not want to touch his property ( therefore laying myself open to complaints ), I have enough space between my vertical fencing to just poke the drain pipe a tads - over the next few weeks eventually edging it over sufficiently for him to have the majority of the discharge.
He is a very difficult person to deal with........hence the caution.
Just like to thank everyone who has given me info and advice - on the thread and by PM.