Commentators have attempted to reveal the reason for the success of 'mummy porn' novel Fifty Shades of Grey.

The book by British author E.L James has become the fastest selling paperback of all time, surpassing the Harry Potter series.

It started as fan fiction on the back of the Twilight vampire stories series and has been trashed by many critics for being badly written.

However, the trilogy has sold more than a million copies worldwide, shooting to the top of best selling lists in the process.

On Scotland Tonight newspaper columnist Martel Maxwell claimed that the "titillating" novels had been a success because the author had managed to "write sex incredibly well".

Film critic Siobhan Synnot also featured in the discussion of the erotic book where she said she felt it was "not anything terribly new" but had been facilitated by the added privacy e-books and new technology provides.

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