Yes, they can. If your neighbor(s) disagree with the proposed works then they can refuse to consent, however this would then open a formal dispute resolution process, which can delay the work planned. When this happens a surveyor will need to be appointed, such as ourselves, to help resolve the dispute by ensuring the needs of both parties are met with a revised party wall agreement. Your neighbour cannot stop the works taking place. The Party Wall etc Act 1996 is designed to support development not stop it.