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,

But what is the 'mainstream'? Well women tend to be the majority of book buyers so it's safe to say that the general readership follows the same demographic. But in genre the female readership seems to be in the minority. There's a more equal balance in fantasy readers with about a 50/50 split - but SF, horror or graphic novels do tend to have a much stronger male readership. So that's part of your problem right there...

The other difficulty is actually reaching the mainstream. Something that is incredibly difficult to do when the majority of genre books are placed on SFF specific shelves, or sold online which is not as attractive to your average book browser.

So is an SFF project reaching the mainstream down to pure commercial success? Well yes, to a certain extent it is. Once a genre novel has been televised or filmed, you can almost guarantee that non-genre readers will give it a go. It's much more visible. A similar effect occurs when novels gain a literary status. Take Station Eleven, or The Time Traveller's Wife, The Handmaid's Tale - all could be considered genre novels but they have reached a considerably wider audience than the usual niche due mainly to their treatment in publishing, PR and marketing who have specifically aimed them at a more general readership.

And it can work - look at some of the fabulous books out over the last few years - The Girl With All The Gifts, The Martian, The Shining Girls - all have reached a level of commercial success that is outside of their normal genre fans. I know, from personal experience, that most agents, publishers, TV/film producers are all enthusiastic about finding that next big crossover novel.

The hurdle for any genre book to becoming a big commercial success is the engagement of the mainstream - and it's an incredibly difficult readership to pin down. The biggest frustration still is trying to work out how to encourage all those film and TV watchers who will happily indulge in the entire boxset of  Battlestar Galactica that they would actually enjoy a science fiction novel. Why are they not reading Peter F. Hamilton?! Or how many millions $ are made through the Marvel and DC characters from an audience who, for the vast majority, will never pick up a comic book or graphic novel.

However, on the whole I am encouraged. The more shows like Doctor Who, Jonathan Strange and Mr Norrell, The Returned and Wayward Pines that air and start drawing in new audiences, the more likely that audience will be, at some stage, tempted to pick up an equivalent in book form. And we cannot underestimate the power of social media can have - it's that word-of-mouth phenomenon that can propel any novel into the mainstream if there's enough traction and excitement behind it!

There's no doubt in my mind that genre is already making great leaps and bounds into the mainstream. I'm just looking forward to seeing even more of it!