Ask an Property Solicitor. Get an Answer ASAP.
Good evening. Welcome to just answer. I am a solicitor and reviewing your question now for you.
If the extension is encroaching onto your side of the boundary line then yes you can object. If however this was on the planning application wing you didn’t object and they are following the permission to the letter, you will struggle to challenge now. If they aren’t following the permission then you should tell them to stop and to do as permitted and failing which you can apply for an injunction order against them for the extension to be stopped. Any follow up please do not hesitate to send your message. Always glad to assist. All the best.
You are we