Whose responsibility? Builder caused damage with knocking out a wall

[fifimummy]

I'll be as concise and short as I can, but I'd really love some advice please 🥺
We're almost at the end of a side extension.
Builder started knocking a kitchen wall out downstairs and I went to the toilet above and had to get him to stop bashing because cracks were appearing before my eyes. He discovered the 1930s house didn't have a particularly amazing steel above what he was taking out...and then he got more support columns etc straight away.....problem is, it's caused considerable damage to the bathroom.....which is the only room we'd actually done some work to before this .....I'm going to try to add photos. It's old lime plaster so not dead hardy I guess.,...
My question is, should he offer to put it right? Or is it just one of those things that can happen with building work and I need to just sort it? I can't close the bathroom window fully any more, the tiles are unseated in places, the laminate floor we put down is buggered at the joins and there's pretty big cracks all around the top of the walls......the room is dusty hours after its wiped over .....we still owe him around £3k for transparency.....but lots of that is for things he says are extras
I moved into my beautiful mum's house (my childhood home) with my kids, after she passed away and I'm so sad about the damage and bloody stress, but also trying to not be clouded by sentimental stuff xxxx
So basically.....who should sort this xx thank you 💖

You say your builder got calcs done to fit a steel after the event.
Was that with your own SE, or someone else?
Did that SE do a site visit?.
I wouldn't say the builder was a cowboy..you have building control who would of passed thier work off at various stages, you must of had plans, SE calc package to submit to building control.
Everything seems to be done correctly with the exception of removing the wall on a whim.
Fact that the builder has compiled to BC for other stages, and realises he needs calcs for the new wall is hopeful..he hasnt just pack up tools and gone..
You do need your own SE to visit and look at damage, ideally with builder there..and BC if you can get them out.
At least you might get a way forward..who pays might be another conversation.
But I wouldn't go in blaming the builder ..it's looks like you are both at fault so compromise might be required..

Unless I'm mistaken but you don't need to render for BC to sign off?