Tom Harris has made a statement on this (link below.)
http://www.dft.gov.uk/press/speechesstatements/statements/implementbrightonmainlinerus

Key quote :

"The key conclusion is that the Gatwick Express will be retained as a non-stop service between Gatwick Airport and London Victoria every 15 minutes. In addition, at the busiest times of day, the service will also run beyond Gatwick to Brighton, doubling the number of express trains between Brighton and London Victoria in the high peak. Unused carriages will be taken from storage and reconditioned to provide the extra trains. At least two extra trains will also run between Redhill and London in the peak. These changes will provide more than 3,700 seats into and out of London at the busiest times."