From the comments:
I can remember debating this when the law first came out. We all said what about the little old lady with her fruit knife or the old man and his fishing knife.
People argued that common sense would be used so inncents would not be prosecuted.
Mark Steyn adds:
Her Majesty’s Constabulary are among the laziest, most overpaid, most obnoxious and most useless in the world.