1994 Jaguar XJ 40 erratic fuel guage and warning light

Sometimes at ignition on the guage will read empty, the electronic display will also read empty the fuel warning light will also be lit, however during the course of driving the fuel gauge will begin to creep up, the warning light will go out and the electronic display will creep up in sympathy with the analogue display until both reading are correct for the amount of fuel in the tank