Neighbour Wants us to Remove Flashing that we Placed Without Consent

Question

We have recently had some roof repairs done on a flat roof of a terraced house.  This flat roof shares a parapet wall with our neighbour.   

As part of this work our builder (unbeknownst to us) put a bit of leading over the parapet to stop water entering the party wall.    Our neighbour, for aesthetic reasons, wants this removed.  We did not know about the Party Wall Act 1996, but in any case did not know that this would need to be done, as it often happens with roof repair.  The neighbour in question is in one of three flats in the terraced house next door.  My questions are: 

1. As we did not follow Party Wall rules, can our neighbour unilaterally remove the repair (lead)?
2. As the work is done, is it outside the Party Wall Act?  Is it possible that we get retrospective agreement from a Surveyor?
3. If we get a Party Wall Plan from a Surveyor, are the subsequent repair costs shared equally?
4. Do the other flat owners who live below her in the building have any right to dispute her removing the lead repair, which benefits them?

Answer

If the lead flashing has been placed over, i.e. on top of, the party wall it would not have come within the scope of the Party Wall Act. If it was cut in to the parapet then it would and you should have served notice. From what you say it appears that the first option applies. If that is the case then you would have required your neighbour’s express consent to lay the flashing any further than half way across the top of the parapet. If they didn’t give permission then they can remove it.  

If the work had come within the scope of the party wall Act it could not be undone and there would be no need to involve a surveyor.  

I don’t think the last 2 points apply so I won’t go in to them at this stage.  

Let me know if I have misunderstood.

Follow-up

Many thanks to you for taking the time to respond to my question.  Your response is very helpful and applicable.   

We are awaiting a response from our neighbour, but hoping it will blow over.