From a simikar source...
http://amazingstoriesmag.com/2013/02/dont-quit-your-day-job-traditional-publishing-by-the-numbers/?utm_source=feedburner

I cannot remember who said this, it was someone perhaps on this site. They pointed out that in the best case scenario, you get a 6 figure deal. That's probably going to be the lowest possible ammount: £100,000. That will be for a two book contract. Assuming a book takes a year to write, you're on £50,000 p.a. before tax and N.I. are deducted. I'm not saying that's not a good salary but it's a long way from being a millionaire, and there are LOTS of other jobs that are far easier to get into and less risky once you're in that pay at least that and more.