system
A chat on subreddit /r/me_irl
human
They sometimes have commercials in between shows but never during.  And IIRC those ads are just promos for what’s coming soon on BBC

The BBC is funded by citizens with a special tax that anyone who owns a TV has to pay.  Because it’s citizen funded they do not rely on commercials to cover costs.  

*Things may have changed since I was last there since they have had a run of conservative governments which are not a fan of the BBC being publicly funded.
gpt
There are never any paid commercials on the BBC the only ones (like you said) are between shows for other BBC shows/channels/radio

Edit: correcting autocorrect