As much as I hate dragging up old threads, it just goes that you should always continue an existing discussion rather than start a new one if the topic is the same.
That said, I can now say that I've tried both the Sanitarium Marmite from New Zealand and the Unilever Marmite from the U.K. I can say that both versions of marmite are substantially the same item, but the flavour of the U.K. Marmite is a bit more punishing. New Zealand's Marmite is certainly more pleasant (if such a thing can be said about such a product). I am about to have to place an order for more as my current supply is almost exhausted.
Now, if only I can get my hands on some Vegemite, I'll be able to tell the full story. Don't bother sending me any Bovril.
