To ask neighbour to pause building work and sort out planning permission and party wall agreement before continuing?

You are not being unreasonable at all . Without it your insurance might not cover you at all . Get legal help asap and call building and planning control asap . Your property can potentially be in danger .

Many many moons ago I worked as a surveyor, and although my memory is hazy, i definitely remember doing party wall work and for the kind of work you’re describing, your neighbours need to hire a party wall surveyor. I’m pretty sure that’s a legal requirement. It covers you both in the event of any damage to your property. A proper condition survey is necessary in relation to your party wall or boundary before work commences.

The party wall act also relates to foundations laid within a certain distance of a party wall if they go down a certain depth past the party wall foundations.

Bloody hell OP, they have taken you for mugs, have clearly employed a cowboy, and gods knows what damage they could do to your property.

Only complete CF's would dream of doing this.

In your place I would order a video bell for the front of your home and a camera for your bedroom positioned so it can record the work being done from Amazon.
They are not expensive and will give you video proof of what they are doing.
One with an app on your phone would be handy so you can check in regularly as to what they are doing.

I wouldn't trust them as far as I would throw them.

I'm sorry that your neighbours are absolute pond life @123MyName321 !

This is outrageous. Have you spoken to the planning department yet? Have the ceased works?

If not do so asap because they are taking the piss.

You don’t want to end up like this poor lady. The neighbour has buggered off abroad. https://www.bbc.co.uk/news/articles/c65y5x2pxpn9o

Surely you must know you are not being unreasonable?

Have they shown you the plans? The very least they should have done is show you that. At least then you know what they are proposing to build.
ref contacting the council, you need to go to the planning enforcement team and building control.
Also get a party wall surveyor instructed, they should have done this before any work started & have an agreement in place. They need to pay for this as well, not you.

I’m a charted surveyor and I wouldn’t hesitate in reporting them to planning enforcement building control. Unfortunately, the council has no powers with regard to the Party Wall Act.

Just report and back away

You should be speaking with Building Control at the council IMMEDIATELY. Don't mess about waiting for XYZ, they could be doing something that devalued your house and you need to protect yourself. You would be naive in the extreme not to contact the Council, that is literally what they are there for.

If they don’t have planning or a party wall, do they have building regs process in place? Unlikely and you can see if you look at your local authority planning.

Report, report, report.

TBH I'm amazed they stopped after you asked them to, but you're doing the right thing in reporting this

Unfortunately it's one of those occasions where "being nice" would never work.
No matter how gently it's put people like this will regard any query about their plans as a confrontation. so you might as well use the official route from the start

We live on a crossroads and the people diagonally opposite told everyone they were going to convert their loft and put in skylight windows. They had planning permission for this - I checked online. They then took the roof off, built a third storey with ordinary windows, and were all ready to put the roof back on when one of their immediate neighbours started weeping and wailing that they'd had their light built out, plus they were now intrusively overlooked (as was the neighbour round the corner).

As she was too nervous to deal with it, I took some photos and emailed building control. They phoned me, just to say "Right - we'll see about that!" and were round that afternoon. The bloke in charge rang me later to say they'd been told to take the whole extra floor off and restore the roofline. The culprit complained bitterly that he had spent £150k for nothing, but it served him right and nobody cared.

Report the builders too, they'll be working for cash which they wont be declaring.

You really need to et onto a named planning officer in your local council. As soon as possible.

Your neighbours are arses to do this with no party wall or planning permission.

Do it. Fast. It’s a huge job trying to sort out ‘omissions’

Well done OP. In my experience, planning officers are, shall we say, extremely keen on implementing every single teeny tiny element of the law to these situations so they will be totally on your side. And don’t worry about your neighbours- they clearly don’t give a fig about you or your property. And no reputable builders would touch this so they are dodgy as fuck as well.

I'm always amazed by what CF's think they can get away with. Hopefully now you've got some professionals involved you've covered yourself for inept and deceptive builders and neighbours

Agreed. A party wall agreement is essential too. Very worrying.

Absolutely not unreasonable, lord knows what you could end up with next to you if you don't step in quickly. Our extension didn't need planning permission but it still needed planning approval