This CDAN guy doesn't sound like either JRM or the Sheffield lad to me. I don't consider JRM to be truly A list as most people I know wouldn't know who he is by name. He's certainly not what I'd call an A list movie star.
The Sheffield lad has the name recognition and the film and TV work but as said by others, he comes across more as a boozer in the football lout tradition than a junkie.
Can't think who else it could be though.