Dispatch from the Land of the Unnecessarily Cryptic

In Kings Cross Station this morning, I heard the following announcement on the tannoy.

"Would an operative please go to the North Ticket Hall, Escalator 17 for a Code 4?"

Having been in the North Ticket Hall not 30 seconds prior to this announcement, I can state with confidence that an 'operative' is a 'cleaner' and that a 'Code 4' is a 'spilled cup of coffee'.

Now I'm wondering what Codes 1 to 3 mean.