Samsung is now rolling KitKat update for the UK Galaxy S4 and Note 3. The update is only made available for the unlocked devices while those on contact would be getting the update in near future.
The update brings in the typical KitKat features and enhancements like the improved lock screen along with the full screen music album art and also a dedicated camera key. Also some of the minor user interface changes and also improved stability.
Also the KitKat updates for the galaxies had started in January and if your carrier has not yet made the update available, you might be getting the update soon now.