According to this BBC article, authors’ income at ‘breaking point’:

Almost half of the money made by professional authors is earned by just 5% of writers, according to a study of authors’ earnings in the UK.
The top 5% of authors earned 42% of all income received by professional writers in 2013, according to The Authors’ Licensing and Collecting Society.
Meanwhile, the bottom half of professional writers accounted for just 7% of all authors’ earnings overall.
The society said last year that writers earned 29% less in 2013 than 2005.
“The creative industries are thriving, generating £76bn per annum, yet professional writers have seen a near 30% reduction in earnings in recent years,” the society’s head of rights Richard Combes said.
“Consequently many are no longer able to sustain a career. The one truly irreplaceable link in the value chain is being stretched to breaking point.”

I wonder if the writers who create the actual words for celebrity ‘authors’, can live off those earnings?