And just to come back to topic for a moment...

I had theft of my carry-on, not theft from it.

The culprit was apprehended before he left the airport and I got my expensive luggage back. My angel? The BA purser, who used her initiative and actually found and approached the thief herself. If she's here, thank you! I did of course write to BA to ensure she got recognised for this.

Moral of the story - no matter how busy the flight is, do not allow your carry-on to be placed in a location away from your seat.