A LandRover Dealer or specialist is probably the best bet, but at a price. If it's not electrical it could be over-fuelling which wets the plugs, & causes a multiple misfire. If there's a temperature sensor which detects a cold start - try replacing that? An intermittent fault on a sensor might reset on restarting. If you can find out where it is - disconnect it while the engine is running badly and see what happens.
There was an incident last year with a Plus8 on carbs, and an aftermarket high pressure fuel pump caused a major problem which meant that it just wouldn't run. So excess fuel pressure can cause this. A blockage in the fuel return to the tank might also cause it.
