Party walls? my neighbour requirements to build an extension using the wall.... i want to refuse to go along with but how? i live in a split horizontal maisonette. i have the underground room...

i live in a split horizontal maisonette. i have the underground room and ground floor. there is another flat above mine. it looks approaching a house from the outside and is semi detached. my basement looks out onto a niche, which means I enjoy good flimsy and use the area as a veranda. the other half of the semi is an exact copy however they own the together house. we both have L shaped ground floors. my neighbours want to use the carnival wall that splits our basement / niche area and build an extension. they want to spread in the niche, meaning that their crypt will be concealed and build a room at ground level over, what would hold been the bay. This means that the shindig wall will be extended upwards. It also means that my bedside light / vision from my porthole on the ground floor will be reduced. the party wall is smaller quantity than 1 metre from this window. What do i do to refuse to go along with it? They say that they do not have need of planning permission.. is this correct? they enjoy informed me in creature????
Answers:    If you live in the USA, they do call for permission. Go to City Hall and chat to an inspector in the Inspection Department.

OR see an attorney as soon as possible in the past they start building.