Mk 4's have never been assembled in the uk. On my car , the front wing panel appears to be deliberately folded over double at the join,making it a removable panel rather than a flush spot welded join. And the gap, also appears specially shaped and free of undersealant, so quite likely a water drain, as suggested by 5thcivic.
I might test it later with a watering can, although according to my wife my appointment at the dentist is more important