“We are aware that a limited number of HTC users are experiencing difficulties with the KitKat update. As a result, all FOTA updates have been temporarily suspended. HTC is committed to providing customers with the best possible mobile experience and we are working hard to resolve the issue quickly.”
There's no info on exactly what kind of issues have been discovered with the firmware, but HTC's UK updates status page once again lists all carrier variants as being in the "integration" stage. If you've already updated your UK HTC One to Android 4.4, hit the comments and let us know how you're getting on.