UK Car Repair: ROVER 75 1.8 CLUB, duel fuel, rover 75

Question
MY ROVER 75 IS DUEL FUEL (PETROL+LPG). IT IS DIFFICULT TO START WHETHER HOT OR COLD BUT IT RUNS OKAY WHEN ON LPG BUT POORLY WHEN ON PETROL

Answer
I presume it starts hard on either fuel!  Normally it should be started on petrol, then switched over to LPG, this is because it should start easier on petrol.  From your description the lpg side is working properly, that would indicate a fuel/fuel supply problem.  Check for bad petrol, petrol filter, petrol pump pressure.