Lawful reason is pretty open to court interpretation. Job or pass time has tended to require actual appointments or indication of intended visit. Carrying in any way as an every day thing will tend to involve it being classed as a weapon.

I have a fairly large knife (far from a sword) strapped to the inner door of my brother’s and my little narrow boat. As on the canals and rivers it is a genuine safety need to cut ropes or remove branges weeds etc.

But even walking with such on the towpath without a direct need has lead to friends arrest.