Just as an aside, I have been caught up with alarm activation at Heathrow.

The airside (arrival) zones were locked to hold passengers in what was intended to be, I presume, a safe area. However, as more planes disgorged the numbers of people grew quickly.

There was no going backward - security - nor forward - locked doors to prevent movement to another zone!

All the time, the alarm bells were sounding and despite the chatter it was possible to hear clearly the recorded <Fire alarms have sounded, leave this area immediately>.

The other side of the locked glass doors was deserted - very reassuring. We were effectively trapped, without adequate information and/or having been misinformed. Eventually, one or two firemen wandered past on the other side of the glass panels without bothering to stop and explain.

It was a surprise that the doors were not kicked down and/or people found their way out onto the tarmac as the crown panicked!