There was no air coming out of the driver sides vent on mine so I took
out the vent (flat screwdriver) and saw that the pipe to the vent was
loose. I removed the bottom parcel shelf (only a philips screw driver
needed) and the pipe had come away at the fan end (central console).
Simply popped it back on (push fit) and then put the vent back in place.

Not entirely sure what had caused the pipe to work itself loose though.

Cheers

D.