I just discovered this kind of thing is available in the US. Is there anything similar in the UK that building control would be happy with? https://joistrepair.com/products/2810hr
There's normally something by Simpson strong-tie, if not you can just make your own from steel or ply gusset plates.
Well ask them what they would recommend if they are requesting the impossible. Ply, glue and screws or steel plate has sufficed for decades.