So at this year's London Book Fair I was invited to moderate a panel to discuss this very question. Joining me were David Bradley, the editor and chief of SFX and Total Film magazines and Rosie Fletcher, the editor of Total Film. It was a lively discussion and the audience seemed to enjoy it but it did get me thinking. What is this 'mainstream'? Is it an invite-only club? What do you have to do to get this collective's attention? And is this 'mainstream' welcoming to genre or do they shun it?

To my mind something has gone 'mainstream' once it's reached an audience who wouldn't normally engage with it. Take the Star Trek franchise - many of its new fans will have never seen the original series. Or Game of Thrones, while some of those watching the TV series may dabble in the books - they probably aren't waiting on the edge of their seats for the next one in quite the same way that the genre community is.

Many of these mainstream watchers/readers will claim not to enjoy fantasy or science fiction and then be slightly bemused as you try to explain that actually the BBC adaptation of Jonathan Strange and Mr Norrell that they are raving about is exactly that,