Our neighbour has submitted a planning application to demolish the house and build four houses on the plot. We are currently objecting, and I suspect it will get initially rejected but he'll end up getting planning for something.
As part of the plans, there would be massive excavations right up to our boundary, and this will be covered by the Party Wall Act. Our house is 2.4m from the boundary and we have a garden wall and a brick built shed against the boundary so he will definitely have to serve notice under the act if works were to go ahead.
Given the scale of proposed excavations, I suspect he would have to underpin our house at his expense (wants to remove 50-70 lorry loads of soil, has already removed 35 without any planning permission 
). There is no subsidence at present and our house is currently structurally sound. It is 1960s, so the foundations should be a reasonable depth.
If this did go ahead and our house was underpinned, how would that affect us in future? Would we struggle to sell and would insurance become more expensive? If so, would he be liable to pay us any compensation for this and would we go through the Party Wall Surveyor or via a Solicitor?