These adverts in Britain. Are they for Marmite? Or for Vegemite? I mean, are they one of these self-deprecating adverts that we are so good at ? Or one of the "knocking" adverts that the Americans are so good at?

They are for Marmite. The underlying message is "Are you tough enough for Marmite, or are you a wimp?" The opposition isn't Vegemite, it's the people making stuff that rots your teeth when you spread it on bread.

I don't think I've ever seen an ad for Vegemite. I think the only people who tend to buy it here as are homesick Ozzies, or fanatical Neighbours fans (if there are any left). Anyway, all the yeast extract Marmite clones taste exactly like Marmite rather than Vegemite, and are dressed up to look the same. I assume it's the other way round in Australia.

I take it the difference in taste is something to do with different strains of yeast used in the brewing industry in the two countries. Or maybe it's because of the sun going round the sky widdershins out there...