Games : Will characters not in my current party gain experience?

I currently have one party member who is at the Inn, presumably quaffing ales, and not in my active 6 player team.

Will this character accrue any experience points whilst they are 'sidelined'? Or will I have to add them to my team and essentially seek out some easy experience to level them up to match the rest of my team?

Or, when I add them to my current team, will they receive a kind of bonus experience to bring them up to the right level?