“The 'agreed' surveyor said that my notice was actually missing some information…”
The information required in the notice is here:
https://www.legislation.gov.uk/ukpga/1996/40/section/3 . So not much.
However, it's worth noting that if you have been exchanging messages with your neighbours through an informal channel like What App without issuing a formal notice, it can still fulfil the Act's intention of encouraging direct discussion between the parties involved, as long as the necessary information is adequately conveyed.
You do not need legal advice either and you are not losing rights to your development.
"he will then use his judgement to see if it is a party wall (it isnt) then he will relay that to them." Regarding the classification of the wall as a party wall, it is essential to have your usual surveyor assess the depth of the foundations involved. If your foundations are deeper than your neighbours', the works may fall under the jurisdiction of the party wall act, even if the wall itself is not technically a party wall. In such a situation, it can be considered a goodwill gesture to involve the party wall framework (not the appointment of the party wall surveyor/dispute process), as being a good neighbour often requires mutual cooperation. I recommend explaining to your neighbours that you are keen to avoid unnecessary costs and entering the dispute process and are open to discussing the matter directly.
Additionally, it's important to communicate that no further actions will be taken until the depths of the foundations are determined through trial pits. This ensures that everyone is well-informed before proceeding. If your neighbours insist on appointing a surveyor when the party wall act does not apply, they would be responsible for covering the associated costs.
It's worth noting that the issue of the boundary is separate from the party wall matter, and any planning permissions obtained are not relevant to this specific issue.
However, based on the pictures you have provided, it appears that your neighbours have built upon your wall, which is causing difficulties for your own construction. In such a case, if you decide to proceed with the agreed surveyor route, the party wall award should include provisions for your neighbour to contribute to YOUR additional costs incurred by the work as a result of THEIR building on your boundary wall. You should inform them of this and explain that they would also be responsible for the costs of the works on their side, which would be addressed through their own counter notice. It's important to communicate that these costs can be substantial and that they would need to contribute to them in the near future. Alternatively, you can offer them an alternative, if unnecessary party wall surveyors can be avoided, you would be willing to ensure that your builder takes care of the necessary steps."