I was in a similar situation a couple of years ago with our neighbours’ proposed extension blocking the sunlight in the part of our garden closest to our house.
I spoke to a friend who is a planning professional and they helped me work out reasonable grounds for objection. The main one for us was loss of amenity as we use that part of the garden a lot. A second one was that the drawings did not show the new shadow on our garden.
I contacted our councillors and sent them photos of our garden and explained how we would be affected.
The number of objections can influence decision of whether the application is approved or not, so each member of the family living at my address objected.
I contacted our other neighbours and asked them to object. Several did.
My councillors were brilliant and spoke directly to planning. Planning required my neighbours first to submit new drawings showing the shadows on our garden. Then I think they must have advised them that their plans were most likely to be refused, because they were quietly redrawn.
The neighbours later resubmitted a greatly revised application which will affect us at all.
So now all we have to contend with is months and months of noisy building work with digging, sawing, drilling, hammering, noisy men’s voices, radio music etc, up to 7pm 6 days a week. But at least when it’s finished our garden will again be sunny and peaceful.
The building noise is awful. My health has been affected. I have tried to remain civil with the neighbours but our relationship is most definitely affected. They have every right to build on their land but it’s hard to believe they spared much of a thought for the impact of their actions on us.