Problem you might have is that for carry-on luggage liquids, pastes, and gels have to be shown sepearately in those 8'' x 8''clear plastic bags at security. I'm sure Marmite would be classed under one of those headings. The limit is 100 millilitres per item, up to a maximum total of 1.0 litre. Marmite isn't packaged in millilitres, but in grams, with the smallest jar being 125mg, and the biggest being 500mg. What security might make of it, I don't know. But if they were being snotty, they could class milligrams as millilitres and confiscate the lot. Your only defense might be this, but it may not work if you have the biggest size jars...
http://scienceblog.ie/tag/airport-security/