You first have to check if the works are notifiable under the Act. If your neighbour is excavating (section 6), building a wall close to the legal boundary (section 3) or cutting into a party wall/structure, then it is likely notifiable.
The Building Owner must then serve notice. If they do not, then the Act can not be invoked (“no notice, no Act”) and you must seek an injunction through common law.
You could still appoint a surveyor to represent you and write to the building owner, informing them of their duties under the Act and that conducting works without serving notice is illegal. This may pressure them into serving notice.
If the adjoining owner’s property is damaged and compensation is sought, then a surveyor or judge would not look favourably on a building owner who resisted following the Act.
If the works have already stated, a late notice could still be served. You can still get surveyors involved after the event once some or all of the works are underway. If there is still some “notifiable” work to be carried out then a Notice can and must still be served in respect of that.
For example, a party wall notice to demolish/rebuild a party fence wall was not served and the works are already underway. Notice can still be served for excavations and new foundations where applicable.
Then, surveyors are appointed and a schedule of condition should quickly be organised before any damage is sustained to the adjoining owner’s property.
If no party wall award is forthcoming, then the extent of legal involvement can vary (including the associated costs) as it can lead to a series of court injunctions lasting for an indefinite period preventing the party wall works proceeding until the building owner follows the Act process.
It would seem prudent therefore to build the party wall requirement into the overall project costs and programme. In some cases, agreement can be reached quickly, particularly if the neighbour consents to the party wall Notice (and thus a party wall Award is not required).
There have been a few legal cases in connection with the 1996 Party Wall Act regarding notifiable works being carried out without there being either consent or an Award. The number of incidents are expected to be greater where there is no Party Wall Award.
It is therefore unlikely that you would be able to obtain a retrospective party wall agreement if works have been completed, even if a notice was never served. This is because a notice needs to be served for the Act to be invoked. Party Wall Surveyors must be appointed under Section 10 of the Act for them to draw up an award for you.
