Thanks for the continued advice from everyone - I used a circuit tester and there is definitely power getting to the fuel tank (the led was flickering, so I'm assuming this is what the flickering from 10v to 0v indicates) - would I find the regulator in close proximity to the petrol gauge.

As the gauge does move (albeit, always to 1/3 full) the uneducated me is going to suggest that it's the sender that needs to be replaced

Got my first ever Morgan Car meet-up tomorrow - so excited !