And what kind of new concession should be offered? That is easy. What Mr Johnson would need to win a second referendum is an emergency brake on free movement of people, allowing the UK to limit the number of EU nationals moving to Britain if it has surged beyond a certain level.
In retrospect, it was a big mistake on the part of the EU not to give Mr Cameron exactly this concession in his renegotiation of the UKâ€™s terms of membership early this year. It was the prime ministerâ€™s inability to promise that Britain could set an upper limit on immigration that probably ultimately lost him the vote.
Sounds logical to me.