Citroën Half-Track, with family and friends aboard, early 1960s

My maternal grandfather, who is at the wheel, had presumably acquired the car in connection with his Citroën dealership. It was used as a shooting brake on his farm near Lincoln. It may date from around 1930 (cf. www.bonhams.com/auctions/17302/lot/283/ ) and I believe that it was bequeathed to the Lincoln Vintage Vehicle Society which seems to have sold it since. Further detail on the vehicle or on its later history would be very welcome.
Scanned from a small print of a rather over-exposed photo.