the price shown on virgin's website (animated ad at the bottom of the home page) currently advertises from �10-00 one way.
I don't know about �9, but you can get a �15.00 return ticket with Chiltern Rail from Birmingham Moor Street, which would be �5 less that virgin's headline fare.
As Mushroom25 indicates, the �9 fare went up to �10 with the last set of fare increases. I've just checked the National Rail site and used the usual criteria to find such fares, i.e. I chose off-peak (early afternoon) trains and selected a date several weeks in advance. As expected, the fare offered was Virgin's 'Value Single Advance C' fare of �10. http://www.nationalrail.co.uk/