Thanks for the information, it does appear the extension was not built to planning regulations.
The extension has become the immediate party wall and is two storeys high.
I have checked both land registries and the deeds / boundary line show that the alleyway and where the extension has been...
Is there a time limit for encroachment?
On receipt of land deeds it has become obvious that the next door neighbour has a sometime taken advantage of a previous vulnerable occupant.
There was an alleyway between the two houses which the deeds show belong to the property we have purchased...