That's what usually does it I only ever have mine on re circ for short periods of time, Dartford Tunnel etc.
**edit** Just checked and the manual says:- "Do not use the recirculation mode for long periods at it may cause the interior air to become stale and the windows to fog up" It also recommends that the recirc mode is only used to prevent the ingress of dust when dust is raised in front of the vehicle. It also suggest that AUTO may be normally used all year round as the system automatically works to keep a constant temperature. Air flow distribution and fan speed are also controlled automatically.