Draught?

I have a new 09 plate Vauxhall Corsa and have noticed that I have a very cold draught coming up from around the bottom of the passenger seat. I know it is nothing to do with the heating because all vents are producing warm air. I know this car is under warranty and I can take it back to garage but I would like to know roughly what could be causing this so I don't look like some dumb female. All help appreciated.