AM General did the same thing. They used a Penta nut on the bead locks.Of course there is only one. How typical of Ineos Automotive.
It is highly unlikely that the nut in questions is specific to the Grenadier axle. It is almost certainly used elsewhere. Given this there is definitely a tool available to fit. The issue is finding it. Why must Ineos make everything so difficult.........
I know Kent Moore Tool made those sockets.