Hi, welcome to GoY, they've gone brown because of the extremely cold winds we had last month, Cordyline australis aren't fully hardy in the U K, they appear to be the leaves from the lower part of the plant, so if it were mine I would just leave it to nature, they will die off as the trunk extends naturally, whatever way you cut them, the plant never looks well, as even if you cut them to as near the trunk as possible, you will still be able to see the stumps of the leaves, it looks more 'natural' if they're left alone, Derek.

Wait a little bit longer, till we're sure the cold temperatures aren't coming back, then trim off the damaged leaves if you like. It'll be a result of the cold weather we had this year...

Thanks very much