The last thing you expect at a Plan B concert is for the star of the show to launch into an anti-drugs speech. But that was exactly what happened on Friday, when the controversial Forest Gate rapper began lecturing the crowd.

But the fans who had packed the home town gig of this post-poned tour need not have worried that their hero had lost his edge. His message was hardly one to delight Nancy Reagan.

The guitar-toting rapper was keen to point out that he certainly wasn't against "all" drugs.

"Pills and weed" were things he had taken, so he couldn't tell anyone not to try those: but crack and heroin, which, he said, had ruined the lives of two close friends, were substances he was strongly against.

It's not something many of the people his language, subject matter and graphic imagery offends will probably ever notice, but 24-year-old Ben Drew is a deeply moral fellow.

Rumour has it that the reason the songs Suzanne and Some1's Switched In Harvey Nicks have only been put on freebie CDs or distributed on the internet is because he feels uncomfortable at the thought of profiting from other people's tragedies.

The first is about a victim of the Camden Ripper, and was played on Friday complete with the chainsaw sound-effects and screaming, while Harvey Nicks talks about the murder-suicide that took place in the store in 2005.

"Some people think I'm just trying to shock you," he said, trying to explain why his songs contain so much horror, sex, violence and excessive swearing. "But I'm just trying to get inside people's minds."

And with that he began thrashing his acoustic guitar, hammering out the introduction to Missing Links, a song filled with images of drug-taking, but which talks about how substance abuse destroys talented kids' potential, and how dealing turns communities into ghettoes.

Yet for all his ability to shock, Plan B's show was rather conventional. His four-piece band's rock leanings tended to flatten out the detail of the songs, and when his guitarist chose to show off, it was with Jimi Hendrix's Purple Haze riff.

Human beatbox Killa Kela joined them for an encore which included a cover of House Of Pain's Jump Around and even a ramshackle run through Blur's Song 2.

Plan B played Sick 2 Def solo, and it provided a glimpse of what might have been. With the song stripped down to its simplest form, and the crowd obediently quiet, it had the sort of power some of the rest of the gig lacked.