If you are an Adjoining Owner and you receive a notice under the Party Wall etc. Act 1996, you will have 14 days to carefully consider how to safeguard your interests. If you do not respond or appoint a surveyor within this time period a further 10 day notice will be served, requesting that you do. The following three options are available to an Adjoining Owner upon receipt of a Notice:
Consent to the Notice: If an Adjoining Owner is satisfied that there will be no damage or consequences to his/her property, then he/she may consent to the Notice and the Building Owner will be able to proceed with his/her proposed work without an Award being necessary.
Dissent to the Notice and appoint your own surveyor: The Adjoining Owner’s Surveyor will liaise with the Building Owner’s Surveyor and will prepare an award authorising the proposed works.
Dissent to the Notice and concur in the appointment of an Agreed Surveyor: If the Adjoining Owner is happy for a single surveyor to represent both parties’ interests, then he/she will act impartially to draw up an Award.
Source - FPWS.org.uk