how can i stop my cordyline rotting any further

These are not completely hardy in the UK especially the red leaved ones. We've had a lot of freezing weather so it may not be too happy. Move it to somewhere protected (up against the house...) preferably a sunny place and don't let it get too waterlogged, put it on pot feet (I'm assuming it's in a pot!). If it's in the ground then you may lose it. Protect it with straw tied round if we get more freeezing weather, don't wrap it in bubblewrap as it will just rot quicker. Good luck with it.

Hi Vickone, Volunteer is right, i had this happen to one i had 2 years ago, i think the frost got it, and it did this, however once i moved it into the greenhouse is did re-sprout from the trunk further down, so i cut down to just below where it had rotted and it did re-grow, but it did'nt last long after that and i did loose it. i hope you have better luck...in my case i went and bought a 'red star' which is fully hardy in the UK, and that is doing fine in my border as we speak.