Marmite is not banned in Denmark, and in my opinion, the British media blew the case way out of proportion.
My personal opinion aside, then the thing is that if you want to sell fortified foods in Denmark, you must submit an application, so that the items can be tested to see if it is safe for everyone to consume. Some population groups are more sensitive to certain vitamins and minerals, some fortified foods contain too high levels of vitamins and minerals when compared to recommended daily doses, and it is possible to overdose some.
So it is a safety precaution. The problem with marmite is that no one has sent in an application for the product to be tested, and if it has not been tested and deemed safe, then you are not allowed to sell it, but it is not banned. If an application is sent in and marmite is proven to be safe, then you can sell it all you want.
And it is possible to buy fortified foods in Denmark. Since 2003, 90 products have been approved, with 30 approved just in 2010.
Here's the official statement from the Danish Ministry of Food, Agriculture and Fisheries regarding the whole marmite business:
http://www.uk.foedevarestyrelsen.dk/ImportExport/Legislation_on_import_of_food/Marmite_not_banned_in-Denmark.htm