Thanks @why_oh_why I'll ask them. I had just hoped some BT NowTV users could shed some light with that concrete example. I'd like to mark your answer as the solution but I don't use this forum much and couldn't see any option for me to mark any reply as such.
I did some checking for you. I have BT Big Sport with NOW Entertainment as an add-on.
Deception is only available live. I can watch and record using the BT Pro Box. It is not available to stream via the NOW app via the Pro Box.
Regarding: The webpage https://www.bt.com/tv/on-demand/now-tv/alibi-tv-channel-whats-on-top-shows-series-how-to-watch-strea... says "Catch up on Alibi TV programmes with the UKTV Play app" - not NowTV.
I had a look on the UKTV app via the Pro Box. Alibi is not a channel listed (only Dave, Drama, W, Yesterday). So any catchup or on-demand of Alibi is via the NOW app.
The BT article is incorrect , Research by the author and a proper review process should prevent these errors occuring but some (too many in my view) seem to occur. UKTV app is only used for the Freeview channel catchup/On Demand. The Subscription channel content such as it is has always been provided by player(s) provided by the subscription provider. As you get Alibi by the Now Entertainment membership that is the Now Player.
Deception is not really a new series , it is just new to Alibi . Research indicates it was ordered by ABC and cancelled after one season in 2018. The likihood is that Alibi acquired linear broadcast rights at a later date but most probably not streaming righrs (but only they can confirm).