HTC is steadily dishing out KitKat to HTC Ones all over the place, and now it's the UK's turn. The company has started the Android 4.4 rollout today, which will continue over the next several weeks. It might not yet be your turn in line, but that doesn't mean there's any harm in checking right away.
We started rolling out Android #KitKat 4.4 for the HTC One in the UK. Settings > About > Software Updates > Check now!