I don't know if blue lid Marmite contains KCl. It's not mentioned on the Marmite website but KCl is frequently used as a substitute for NaCl, eg in 'Lo-Salt' or whatever they call it.
Some products contain much salt, not just for flavour, but also to extend shelf-life, as bugs and moulds can't grow in a high salt concentration.
fuaran's bread probably contains a gram of salt per slice, even before it gets butter & Marmite.