My next door (adjoined) neighbours have put in a planning request to build a single storey extension at the back of the house. This has apparently been agreed. The first I heard about it was when I got a spam letter through the post from a specialist party wall surveyor (NOT acting on their behalf) offering to act for us. I genuinely had no idea there was any planning application at all until that moment. (We get on ok with neighbours, no arguments, but not friends if that makes sense)
Found the plans on the council website, and they've been approved. I called the planning department, because I thought they were supposed to notify neighbours and/or stick something on a lamppost or something, and they said no, it's under "permitted development" so that's fine.
I've had a look at the plans and it's probably fine, but what I'm really worried about is the process. Aren't they supposed to tell us they're planning or embarking on work? What about the party wall stuff?
The extension would jut out the back of their house, over their existing patio (and alongside our deck). We live on a hill, so the back of both our houses is 8' higher than the grass level, and their existing patio (and our deck) is built over a big pile of 1920s rubble (with steps to the non-adjoining side). Surely building an extension on top of that is going to involve some serious digging?
(so not to drip feed: they did a loft conversion 5 years ago, and didn't notify us then either, or do anything about the party wall. We didn't realise until it was too late, they didn't build in any sound insulation (it's literally a brick wide) and now whenever I'm in the loft I can hear everything happening in their en suite. Worried the same thing is going to happen again, only this time it might make the back of my house slide down the hill, too)
What should my next steps be?
(Thanks in advance - NC for this as it's potentially identifiable)