It's a Large Letter it it will slide EASILY through the 25 mm slot. Well what exactly does that mean. If I can get a letter through that slot fairly easily I would probably sent it large letter, but somebody else may say it doesn't go through very easily and say it should have been charged as a packet. And don't forget customers will try and squash the Jiffy bag down so it will go through and then it will gradually expand again afterwards.
No doubt staff do make the odd mistake, but the situation must be compounded by introducing such an imprecise system of measurement.
I suppose it was thought up by some bod in an office and tested with a nice selection of boxes rather than squashy Jiffy bags and socks in polythene(?) envelope that are encountered in the real world.
Still never mind, at least it's something else we can blame the front line staff for
