Ahh I think a double misunderstanding has occurred (it's late and there has been red wine in Shoreditch).

I should not have posted that 'All staff are screened on leaving the secure area'.... they may not be... but my point was that the passenger did not simply leave his bag unlocked and an un-secure area... he had handed it over to a secure area where everyone was screened before entering and therefore SHOULD have been trustworthy.

Indeed there is less security clearance leaving the airside area (though there is still some).