Tim Q
The missed approach alarm is pressed by the tower arrivals controller in the event of a go-around. It sets off simultaneous alarms in TC, Thames Radar and Northolt and is paticularly useful in the event of an unexpected go-around.
The standard missed approach is designed to keep the go-around away from departing traffic (for example with comms failure), however the departures and arrivals controllers tend to be more proactive, providing early turns, altitude restrictions etc.
The worst case scenario, is CSA going round off 09L with radio fail and not following the standard missed approach(as it didn't in the TV show) and the northbound departure off 09R getting airborne and switching over frequency to London before being instructed to.
