New key has been sourced.
Most of these roof rack and roof box keys are 'N' series, but this wasn't the case for the Ford rack. It was almost a mirror of the N key blank shape.
The N046 and some other common x046 types didn't work, but the locksmith hit the computer and paper catalogues and - with a couple of trips back and forth to the car to test blanks - he finally got it after about 15 minutes.
'FH' series key, so I needed a FH046.
Pretty bloody good! R & R Security, South Ealing Road.