Chances of successful action on the basis of the accuracy of the fuel gauges is zero.
'Everyone knows' that aircraft fuel gauges are hopelessly inaccurate. They have done for 40 years. Given that public and general knowledge, how on earth are you going to persuade a court of law that you, in trusting such a device and ignoring the POH and various other cross checks, were not negligent?
Now if the aircraft had a fuel system that was advertised or promoted on the basis of absolute accuracy you might have a case - but you would have to prove that is was n't accurate - which given that it would be certified to allow it to be fitted to the aircraft is going to be a pretty uphill battle. Much more likely you didn't do something i.e. lean, monitor, put enough in, whatever, it would again come back to you proving you were not negligent.
Which in part leads back to why the CAA are generally on a 'good wicket' when they prosecute in these cases.