That does not mean that police officers have a duty or obligation to arrest (or even report) everyone they suspect has committed a criminal offence.
Nor does it preclude the exercise of common sense.
After very publicly having turned a blind eye to a major jewellery burglary, I can imagine that one cannot expect the Met to use common sense for anything that risks public attention for quite some time.
So check very carefully before carrying any knives anywhere near London! (I would suggest that buying kitchen knives 'on line' might be the best way to go about such purchases, so that the delivery man is the one who risks 'being in possession' of those knives while they have to transit through 'public places'.)
Here's hoping there will be no unnecessary repurcussions.
... unless "Mr Plod's" actions are proven to have been inappropriate, then there have already been 'unnecessary repercussions': to all of those passengers who could not fly that day.