A few questions for you: 1, is it in a pot, and if so, how long has it been in the same pot? 2, do you feed it and if so, what with and how often? 3, is there any deformation of leaves of any kind, and what colour is it if it isn't green? also, what part of the UK are you in?

All I can tell you is that one of my box cuttings died but didn't lose its leaves. It is still sitting in the pot with brown leaves waiting for me to throw it out.