Tbh I didn't even think about it until you guys started questioning, looking at the gov website (link below)... I am not sure how it was done, but I do know previous owner had it registered, had the sva and had it checked out with the police (local authority were very interested in it apparently as couple of the pcs did off-roading too)...
Any advice on the wading kit?!
https://www.gov.uk/vehicle-registration/radically-altered-vehicles