On the gunboat issue: it is slightly more complicated than Boris sending them in on election day, because he could only send them in response to the French fishing fleet. And they were entirely free to choose what day the action took place. It could be the day after the voting equally easily as the day before. Had it been the day after, Johnson could have sent the patrol boats and it would have had no impact on the votes, because they would have been cast already.

I would say, though, that given the French had decided to turn up just before the vote, Johnson almost certainly reacted by sending in the patrol boats because it would 'sell well to the Brexit supporters' who were about to vote.