The 27-year-old British star - who originally tried to make it in the R&B industry before turning to rapping - explained while he didn't sell "hard drugs", he used to deal cannabis until he recorded his debut album 'Who Needs Actions When You Got Words'.
He said: "I already knew I wanted to do music but I had this other side to me that said if anyone f***s with me it's OK to go and stab them.
"I did something illegal because I was on the dole. I didn't sell hard drugs. I just sold spliff and I feel the same way about that as I did then. I think a bit of weed is fine and it is no different to alcohol."
However, the 'She Said' hitmaker - real name Ben Drew - admitted he still feels anger towards his father, who walked out on his family when he was just a child.
Plan B added to Britain's News of the World newspaper: "He denies everything - all our memories of him, anything negative. He said it's just distorted versions of the truth my mother implanted in my head.
"I'm a grown man and the guy was coming to my house talking to me like I was six years old, telling me not to swear. I'm like, 'You're lucky I didn't smash your f***ing face in'.
"He wasn't in my life and it was his decision. Now he's not in my life and it's my decision. Finally, I got what I wanted - closure."