Decomissioning and Removing a Lateral Drain

[rhino.fog]

I am about to build an extension which would build over an existing lateral drain. To avoid that I propose to redirect the lateral drain around the extension. This connects an adjoining property to the sewer on the other boundary across the back of the house.
However, I am aware that this drain is not in use. The adjoining property had its kitchen moved from the rear to the front of the property 30/40 years ago.
Is anyone aware of a process or what steps are needed to de-register such a drain.
I assume that as it is still there, in theory next door could renovate and put in a basin / toilet etc and on finding the drain, reconnect to it. Would they have an expectation that it is still live. If I can block it up and remove it as part of my extension work then I won't have any build over or redirection issues at all.