Owning your own home

It’s a Victorian terrace that was divided into two flats in the 80s.

Would have put money on this being the case.

I've never worked in Hackney so have no experience dealing with them.

If you can get the tennents to feedback the sound transmission issues to their landlord and work at him from the other side you may achieve something. At the end of the day he is likely to have an easier life going forward if he has to re-let the flat by sorting this now.

the proposed works include quite a lot of structural works including large steel beams, and this has the potential risk to be quite invasive to your property.

Estelle raises a valid point here to put it bluntly I would have serious concerns letting my family stay in a property that had this type of work going on within the building.