Loft conversion and neighbours, advise please.

[junowiththegladrags]

So... three weeks in to our loft conversion neighbour has decided he doesn't agree with the work. Apparently when the party wall agreement was signed he only looked at the drawings on his phone and didn't realise the party wall would sit where it does.

We have planning permission, party wall signed by him and builder has followed the architect's drawings to the letter.
Neighbour wants it a change that if we implement would cost us approx £1000 and a weeks work.

This morning I had him and his slightly aggressive builder mate at the front door demanding work stop immediately. Their well reasoned argument being that our architect and council planing dept are plain wrong. A lot of waffle about his protecting his elderly mother who actually owns the house and mutterings of lawyers rounded it off.

Sounds like a no brainer but we really don't want aggro or to fall out if at all possible.
Anyone know what, if anything, neighbour can do?
Would anyone make the change for sanity or should we polite tell them to dream on and take more notice of what they're signing in future?

Thanks in advance.

I would tell them they need to speak to a solicitor, and carry on as normal.

This will delay things from their side and hopefully stop them coming round and being horrible to you. Since everything has been signed and agreed there isn't actually anything they can do (AFAIK - I'm not a solicitor).

OR
Tell them you will consider making the change (if it's not to your detriment) but they will need to pay for it - in advance.

Thanks Twitter. It's the spectre of aggressively unhappy neighbours that's my worry.
Perhaps if he has to pay out for a lawyer or for the change he'll go quiet.

my only concern would be whether he'd be able to sign the party wall agreement if his mother owns the house (does it have to be signed by the homeowner? I have no idea). Does he has power of attorney. Sorry, I'm know I'm not helping.

I cant see he would get much joy from the planners if they have signed off on it and he has signed the agreement (his fault if he didnt look at it properly).

I think the only way he can actually stop the work is if he gets an injunction on it. Which would take him weeks.
I'm not sure where you sit re him signing PW agreement (is he resident?) if his mother owns the house.

To be honest though, the window for him to comment on or object to the plans has been and gone. I suggest you outline to him the costs involved in altering the work, and say that you will consider reworking your plans if he wants to foot the bill, but otherwise you will continue with the planning that has been granted and which he has signed an agreement for.

Thanks all.
Re the signing, when we spoke to the owner she asked that we go through her son and daughter. That seemed reasonable and obviously we complied. Didn't think to ask whether they has power of attorney as she's still lucid just frail.