Hello. Different expert here. I see that you have been waiting for assistance. Please allow me to add some input. On these cars, the main cause of the dash lights flickering is eithe a loose alternator belt of a faulty alternator (assuming your misfire is not causing the RPM to drop substantially).
Engine misfires on these cars are common. There are quite a few vacuum lines under the bonnet that can become weakened with age, and develop pin hole vacuum leaks. It does not take much of a vacuum leak to compromise your idle quality. Assuming the engine is in a proper state of tune (good/new plugs, cap wires, rotor, etc), If this car was in my shop I would be looking at each and every vacuum line in the engine compartment for cracks, brittleness, softness, poor fit, etc. I have worked on a lot of the MG product over the years (I own an older Lotus), my experience with these issues leads me to believe your major concern is vacuum issues. It is also possible that you have a vacuum leak at the intake manifold gasket or under the carb.
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