At what point does control responsibility for an arriving IFR aircraft formally transfer from Approach Control to the Aerodrome Control Tower (TWR)?

1. When the aircraft is in the vicinity of the aerodrome, has visual reference to the ground, or is established on final approach at a designated reporting point/fix as agreed between the units
2. Only after the aircraft has touched down and activated thrust reversers on the runway
3. Immediately when the aircraft crosses the outer FIR boundary
4. When the aircraft enters the holding pattern at the initial approach fix