HTC One's Android 4.3 update is on schedule and has begun rolling out in the UK. Although the update has been floating around for quite some time now. The new update brings Sense 5.5 UI which adds new features to BlinkFeed with recommended news. You can now also keep articled to be read later.
The update is 675 MB in size and available OTA, therefore we would recommend downloading it over Wi-Fi. Other markets are going to received the update soon and do keep a lookout for that system update popup.