Is the OBD port problem due to lack of power at the OBD port or lack of coms? Same question put another way - Is there power to the OBD port? Does it's power pin use the same fuse as something else e.g. cig lighter socket?
Another thing that can prevent coms on the OBD port is if the LPG system is connected to OBD. This wouldn't be the case with a pre 2000 year Landrover vehicle but the LPG system may be connected to OBD on a post 2000 year Landrover. One way to test for this if just to disconnect the LPG fuse, see if the OBD port starts working again.
Good calls by Gllbert and Symes. Some systems do have separate injector driver units that can fail... Would add I have seen plenty LPG ECU's fail in a way in which they don't connect petrol injectors on a cylinder (or several) when they're supposed to (they're supposed to when the engine is running on petrol). On some (older) LPG ECU's such as older AEB2568 / Stag based systems this can be due to a bad internal relay, I have an old AEB2568 here at the moment that has failed in this way... some day I'll get around to changing that relay so I'll have an extra spare AEB2568 ECU.