Lawful Excuse or Reasonable Excuse is the exact terminology, a Police Officer would apply to finding such liquids/knives/weapons in your possession.

Clearly, the way they were being carried or concealed would also have a major impact as to your being arrested, cautioned or indeed reported for summons.................
ie Travelling to an approved club range or authorised land, with weapons and ammunition duly covered, with a Firearms certificate or copy to hand, would be deemed as a Lawful Excuse.