Advice on neighbour's extension and impact on my property

[Wonderbug81]

My downstair's neighbour is getting an extension done directly beneath my flat. We have a party wall agreement for removal of two chimney breasts at their level but the two surveyors involved agreed no other PWA was needed.

Separately, one of my windows is in a room directly above where they're extending their kitchen into the garden, is no longer fully shutting. The handle won't close properly and it won't lock either. I've also seen some minor cracks around the frame.

I was assured the back wall wasn't being knocked down, they were just removing the double garden doors so no major work to that wall but they have done a lot of drilling so I'm not sure if that's created movement.

The surveyors took photos before the work but what else should I be doing now? And was this likely preventable?

OK thank you. I think I'll call building regs after speaking to my surveyor to find out what they've been keeping track of.

Building control tend to react when builders notify them that certain works are about to happen
For example
The builders may tell BC that they are about to dig / lay the foundations. They’ll ( or they should ) give a date for this. If BC want to visit they can. It’s an invite really. They may however decide the agreed depth is enough.
But yes, I would agree you can ask what they are looking at but they are not obliged to tell you of course.
If your query relates to the PWA your surveyor would stand a better chance of getting a response.

As an aside for this type of extension they will be looking at
foundations
Insulation and U values
Presence of dpm / dpc
Affects on fire safety compared to the existing escape routes ( as its grid fl that’s hardly much of an issue though )

This is really helpful thank you! Feeling a bit out of my depth.

Quick update. Surveyor visited and inspected. They've actually made the door opening downstairs (by the extension) smaller, not bigger so it should have more support but in the process of adding a lintel (which I didn't realise was being put in) there may have been some movement.

Surveyor isn't concerned and said it sometimes happens. They'll adjust the window and repair the cracks (once building has settled a bit).
Report

Yes that could easily cause movement
Excellent news there’s no issues re repairs

That’s great that they are going to do the repairs without any fuss.