The BBC's political correspondent Robin Brant said this was a strong message about what the PM saw as the limits of ever-closer union with Mr Cameron referring at onepoint to "we sceptics".
As if to prove the point, when we go to Winchester University students' union midweek "bop", one girl politely introduces me to her parents who have come along with her.
Mr Johnson told BBC One's This Week programme the low point of his week had been "the rather depressing news that every trade union, apparently, is going to oppose AV in the referendum".