WE DONT LIKE TO BE ALARMIST BUT...
Disasters can happen and if they do you will wish you had a Party Wall Award in place.
Below is a picture from an article in the Daily Mail
Whoops! Families forced to flee in the middle of the night after extension causes the house next door to collapseRead more: http://www.dailymail.co.uk/news/article-2105932/Family-flees-collapsing-home-neighbours-extension-causes-crumble.html#ixzz4dsgZXX4D
Suspicion is that the foundations have been undermined by the work next door. It is too dangerous to go and look around