In normal everyday circumstances, someone like John is soon sussed out. Unfortunately, in an atmosphere like the BB house where most people start off feeling vulnerable, his faux concern and enveloping love for all, can seem like a lifeline. However, I imagine most of the housemates saw a bit of the real John after his pontificating about Darren. Especially as Darren didn't, quite rightly, let it go right away.
What Darren has achieved is absolutely monumental, and if mentioned at all, should be lauded. A recovering addict will forever feel fragile and vulnerable. They have been to hell and know that they are only one drink/fix away, at all times. To play on those vulnerabilities is emotionally abusive.
I hope that Darren can take the attitude of F*ck you mate, I'll show you! He can do this best by distancing himself from John, but I fear he may still see him as a friend.....which he absolutely isn't. He's a conniving, manipulative narcissist.