Christmas cake in the UK is started months before the holiday. The rich fruit and nut cake is "fed" with brandy or whisky - a few spoonfuls at a time, every few days for weeks.
Before Christmas, the cake is enrobed in a rolled layer of marzipan and topped by a thick layer of rolled white icing. Then the whole thing is neatly wrapped in a red ribbon and topped with a holiday picture.
In effect, by wrapping the Christmas cake like a present it is sealed airtight in all that marzipan and icing. That, plus the amount of alcohol it has absorbed, should make it last a very long time. And, kept in a biscuit tin or a plastic food box with a sealable lid, Christmas cakes have been known to be edible for months, even years.
The Christmas cake is not usually part of Christmas dinner but is kept to be offered at tea time and for snacks during the holidays.