Food, cursed information
Apparently marmite has different recipes for the different size containers of marmite. According to their website the 70g container is the only type that is vegetarian (all other sizes are vegan), and it is kosher whereas all other sizes are not.
Food, cursed information
Ok fell down a rabbit hole and found out some more info:
> Explaining the reasons why Marmite products could not previously be heschered Rabbi Conway said: "Bovril, which is an animal extract product, is made on the same site so there are some complicated halachic issues. A key point is that the 70g jar is packed on an all-kosher line."
Source: https://www.thejc.com/news/uk/marmite-is-kosher-again-1.67154
So that explains why only the 70g jar is kosher, but not why it is not vegan
