Diesel smell in cabin

[OscarIndia]

Just wondering if anyone else has had this issue.
When starting up or sitting in traffic I'm getting diesel fumes in the cabin through the aircon.
Fine when on re circ, but still an issue.
Any thoughts?
Passat B7 2.0tdi

[OscarIndia]

I'm assuming either a gasket or something similar, just a case of finding it!