TCAS FAN. The airport may well be talking with their CAA aerodrome inspector behind the scenes. The formal submission of the CAP791 to the development team often happens just before the work commences. The safety case needs input from the contractor so difficult to produce it a long way in advance.
You are correct regarding AIP updates - they take a while to work through the system so may even precede the approval.
Not just a ground survey but a flight survey required too and I would suspect some kind of impact assessment on ATC services. If memory serves me, that's no less than three different CAA inspectorates.