can next door build an extention on my boundary with windows facing directly into my property

A simple answer to your question is no they shouldn't build on your boundary and also shouldn't have Windows face in your direction. Hope this helps Nick

According to the council restrictions if your neighbour is within the limit of your space and it doesn’t have at least 1m distance, is not allowed to have windows on the side that’s facing into your property. Also about building an extension he/she will have to get approved application from the council in his area depending on the surrounding a lot of times can be rejected.