The 16 year old was very lucky to get away with just missing his flight at LGW!
Normally in such circumstances, (regardless of which airline or handling company is involved) the offender will be asked to repeat what has just been said (viz: "I have a gun in my bag").
If he/she does repeat the statement, the police are called who will, usually:
1. Arrange hand-searching of baggage
2. Formally arrest and arrange strip search of offender - a most uncomfortable and embarrassing experience.
3. Ensure offender remains in custody long enough to ensure all flights to the required destination have departed for the day!
To those who see this offence as a trivial issue, there are some of us still working in aviation who have lost friends, relatives and colleagues in terrorist incidents. Believe me, ('cos I have first-hand experience) of all the flights you check in day in and day out, when an "incident" occurs you can remember every face you dealt with!
My son knew from the age of three not to crack jokes about air crashes or hijackings (or train crashes, if travelling by rail!) It's very unpleasant for anyone in the vicinity who is nervous!
As stated in another thread, IF A 16 YEAR OLD DOESN'T KNOW HOW TO BEHAVE IN PUBLIC, BLAME THE PARENTS!!!