Thanks for the replies. There aren't carbon filters on the fan so I don't think it is recirculation. If it was then the white boxing is even more baffling.
I checked above the metal plate outsideand there isn't a vent.
The cement patch to the right has been done recently - our builder said it...
I have inherited this Lamona cooker hood, which has ducting towards the external wall but then there is no hole outside? Is this a mistake?? Where else could the extracted air be going?