Next door neighbour developing to boundary wall and blocking light

Doozergirl

There is something called the Right to Light. It isn't the right within planning legislation, it's an old law that is separate from the planning process.

It's unlikely that you could prevent an extension from being built next door, but there is a potential for damages being paid based on the injury to the existing light. It's based on land value, so unless you're in a high value area, it often isn't worth the stress and cost of employing professionals to deal with it.