Fuel cut Inertia Switch.

[Bigbaldybloke]

You need to know what type of fuel pump you have, if it?s a positive displacement one, I believe these act as a shut of valve and will not allow fuel to free flow through it. Other types may free flow fuel when de-energised. I reckon the carbs on a plus 2 are almost level with the top of the tank so it would only be a problem if the tank was brim full. This supposes any leak is from the carbs, in an accident the fuel system could be damaged and leak anywhere so ideally a shut off solenoid valve would be directly on the tank outlet.