You have to be pretty conservative to get 400 as indicated by Danno ( Welcome to the forum by the way)
I have a 2004 2.0 ltr Sport Saloon and a heavy foot. So on average I get 32 mpg. I never let my tank get to the point where the light comes on, but just recently I did a little experiment.
I filled up and then drove like a granny for the duration of the tank. After calculating this out I did 35.9 mpg and a total of 410 miles before the light came on. At which point I refulled.( I couldn't stand it any longer

)
So the 400 mile barrier can be broken provided that 1. You dont like acceleration & 2. You never exceed 70mph.
However if this is the case then DONT BUY A SPORT MODEL LOL .
The Zoom Zoom factor is just far too much fun to be conservative.