It is debatable, whether BBC conteht is free of ads.
When iPlayer was last working for me, a couple of days ago, I selected some show only to find they had introduced 30 secs of promotional garbage for other rubbish, before start of the show. I was allowed to skip, but my threshold of irritation had already been breached.
Also, after watching some other show, it got “collapsed” into a small window during rollout of credits, filling the screen with adverts for other shows. Live TV BBC is even worse, when an announcer starts yapping during the credits, advertising other programmes, when I might actually be enjoying the fade-out music.
I do agree though that 4od is worse. I remember trying it briefly a while ago, before sign in was required, and instantly dismissing it as useless, as it was litered with huge long advert breaks that I couldn’t skip.