The Party Wall is normally a dividing wall or fence that is constructed on the boundary line generally between 2 properties. To work on the Party Wall for maintenance or say installing steelwork for a domestic loft conversion you WILL NEED to issue notice and gain approval from your neighbours prior to doing anything! Normally the notice period in 30 days.

A building owner proposing to start work covered by the Act must give adjoining
owners notice of their intentions in the way set down in the Act. Adjoining
owners can agree or disagree with what is proposed. Where they disagree, the Act
provides a mechanism for resolving disputes.

The Party Wall Act is separate from obtaining
planning permission or building regulations approval.