Of course to show a knife to somebody else, "flashing it" is a perfectly valid reason. How can they see it if they want to without it being in the open. Sheer nonsense that the knives etc must be concealed and secure while travelling in the car. legal is legal and if there is an exemption or valid reason then they could be surrounded by spotlights and still be legal. The real problem is police ignorance or wilful abuse of power.