Hi,I have a cordyline in my garden that I planted about a year ago

Not sure what you mean by 'along the top'. Do you mean the leaves at the very top, where the new growth comes from, are yellowing? Or that older leaves, lower down, are yellowing?

the yellow leaves are certainly higher up on the plant. i don't think its the new growth that is yellow though. i gave them a slight tug to see if they would come away but they are most definitely very strong (not sure if that means anything?) i also checked along the very bottom and those leaves were just dry, which came away very easily.
i'm certainly no gardener and have only planting things for a little while so any help would be happily recieved and appreciated.
thanks in advance.

At this stage, it hard to say what's happened - it might be that the cold snap in February has affected the growing tip of the plant, and that's why the top leaves are changing colour. I'm afraid you'll just have to wait and see - the test will be whether new growth emerges at the top.

thanks for the feedback.