In a single stair restaurant comprising:

Ground floor open kitchen and dining area, First floor dining area and a Second floor comprising staff changing facilities and a store, can lobbies to the protected stair be omitted with the addition of AFD?

Fire safety guidance recognises the provision of a protected lobby to the staircase should ensure that the stairway is always available during the vertical escape phase of a premises fire evacuation. This is very important when only one staircase is available which should ensure that the staircase will be maintained free of heat/smoke by the provision of “two door protection” between the stairway and the place of fire risk, which will not be achieved by the provision of AFD alone.

It is impossible to give a definitive answer without a fully understanding of the premises and you would need to contact building control for their views on your proposals.