Yep, looks like either somebody forgot or it is deliberately absent on the older hardware. We’ve got one black and two white boxes, it was easy to add on the black but conspicuous by its absence on both of the whites.
Looking closer, the black box had its last update in January 2018 wheras the whites were last updated back in June.
The white boxes are barely adequate when running NBC iplayer but quite ok on everything else. Judging by our old Youview box, the UKTV interface is relatively lightweight so I can’t see why it can’t run on the white boxes.
