A couple of unmanned RIB's purchased from a local seaside resort This could get interesting but I fail to understand how this will protect them if the switch is on land over in France. And why don't they have electricity lines run out to them from the UK if UK territory. Another interesting thing here is that Jersey is a Tax Haven so if there is no power how would this affect bank transfers.
I thought that a good portion of the South of England received its energy from France. They could threaten to cut off the mainland if they really wanted to make a point. Another example of the feeble minded governments we have had to tolerate over the years allowing power supplies to fall under the control of other nations.