Update:
my son has been informed the builder has sent the SE calcs to BC. No idea who the SE is or what the calcs contain / are.
I can only assume the calcs will confirm what the builder has built is correct, otherwise he'd be back changing things.
Will BC check the calcs are "safe" or is it just a tick the box exercise ?
Most of my work over the years has been for 2 LAs. Both had their own in house SEs,
One moved on about 4 years ago (not sure if he's been replaced), the other has just retired. All submitted calculations were always rigorously cheched.
I had a similar kind of situation to yours on one of my jobs where the "builder" altered things (with the client'ssort of agreement but without reference to me. He changed a flat roof support beam to accomodate a wall removal. He did get an SE to design the beam and he did fit the right size. What he didn't do was put in the bigger roof joists now required for one side as thr beam was no longer central.
He only had BC out once to check formation so they were unaware of the issues. The whole thing was like an episode of Rogue Traders.with a massive amount of remedial work required as he had ignored my drawings left and right, mixed up steels etc, etc.
I have to say that BC were really helpful, working with me and the 2nd builder to sort things out as simply and economically as possible.
For this sorry mess of your son's
-IF there are calcs to justify what your idiot builder has done, (must include padstone details)
-IF BC are happy with them,
-IF this SE is properly qualified and properly insured (check what professional body he belongs to)
-IF he inspects the work done and confirms in writing it fully complies
Then it's actually difficult to see what can be done. There would be no contractual basis to terminate his contract because all the work is OK indeed you could become liable for loss of profit.
I don't think for 1 minute, nor ! suspect does anyone else who''s contributed, that all those IFs are going to happen