If its in a pot, remove it somewhere bright but frost free. If its in the ground, pull all the foliage upright and tie in that position and then wrap fleece round the whole thing, two layers, including the trunk. You will need to remove the fleece and untie during milder spells, and don't do it until you have to, i.e., it's going to be very cold. Most Cordylines have been fine for about 12 years, up until the year before last when we had a cold winter, and last year even worse - and according to some experts, this year will be even worse than last. In a seriously bad winter, you may lose the cordyline despite tying and fleecing, especially in the midlands or north of the country.