It's time to get used to the idea of living under Prime Minister Boris Johnson

'He is like a hurricane far out to sea. No one knows where it will hit, or how many roofs will be ripped off, or if we will all get through it. But we know it's coming.'

It may not be long until this man takes the keys to Number Ten (PA)

Boris Johnson is close to carrying all before him. An MP summed up the party’s view to me: “He is like a hurricane far out to sea. No one knows where it will hit, or how many roofs will be ripped off, or if we will all get through it. But we know it's coming.”

All right, all right. That was a Labour MP talking about the imminence of Gordon Brown as prime minister 10 years ago, in October 2006. But it was just the same, only without the menace of Brown’s kneecappers and knucklebreakers. At the time, it wasn’t clear that Brown would be the only candidate. In the end only John McDonnell tried to stand against him, and he secured only 29 of the 45 MPs’ nominations he needed.

Johnson’s landfall is not as certain as Brown’s was, but I have the same feeling now that the other options are narrowing. It is getting harder to see how Johnson could fail to become prime minister.

The first and quicker route would be for the British people to vote to leave the EU in three months’ time. David Cameron may want to stay on to negotiate Britain’s exit, but I do not think his party would let him. In the last few days the number of Conservative MPs declaring for staying in the EU reached 170, which is just more than half of the total. However, that also means that nearly half of Tory MPs are Outers, which is not only far more than Cameron expected, but they have the support of a large majority of party members. What is more, if Cameron loses his great referendum gamble, he would be a failed and broken leader. Johnson would have the authority to insist that the consequences of voting to leave the EU should be managed by someone who believed in it.

As for predicting the outcome of the referendum, I know that guessing what will happen next is what this column is for, and this one is all about predicting that Johnson will be our next prime minister, but I know my limitations better than I did this time last year. The betting markets and the opinion polls suggest we will vote to stay in, but I am not so sure.

If we do stay, though, the Johnson hurricane is still coming this way. Those Conservative Party members, the ones who are overwhelmingly opposed to EU membership, would respond to defeat with the same respect for the sovereign wisdom of democracy as was shown by the Scottish Nationalists 18 months ago. That is, they would immediately declare a moral victory and start campaigning for another referendum. More importantly, they would believe that the world owed them compensation, and one of the forms this would take would be the succession to the leadership of one of their own.

The rules of the Tory leadership contest provide that the final ballot shall be between an Inner and an Outer, and that the Outer shall win. Naturally, that is not quite how the rules are worded but, given that Tory MPs select a shortlist of two and party members have the final say, that is how it will work. (It will be, incidentally, the first time that non-MPs will vote directly for a prime minister.)

The only question, therefore, is who the Outer candidate will be. Something untoward could happen (when I wrote about the imminence of Brown as prime minister a decade ago, I said I didn’t know how the voters would respond to a choice between him and Cameron at the ballot box: I had no idea that this choice would be made after a global financial crisis). But if the choice of Outers is between Johnson, Michael Gove and Liam Fox, Johnson would just about edge it.

It took a former Labour Party official to pose a more important question last week. Tom Hamilton asked if there were any “sensible, non-popularity-based arguments” for why Johnson wouldn’t be a useless prime minister. To which my answer was that he hadn’t made a mess of being Mayor of London, which sounds flippant but isn’t. Not making mistakes is, as George Osborne could tell you, an important quality in politics. Martin Hoscik, the Mayorwatch journalist, said that this was “more to do with the team around him”. But even that is only another argument in Johnson’s favour.

Since Johnson came out against the EU last month, I have detected a change in mood among journalists towards him. The most notable example is an article in Saturday's Times by Matthew Parris laying into Johnson's "casual dishonesty, the cruelty, the betrayal; and, beneath the betrayal, the emptiness of real ambition: the ambition to do anything useful with office once it is attained".

If anything could make me approve of Johnson it is Parris's savagery, an extreme example of the pro-EU journalistic consensus. Johnson blustered inarticulately on the Andrew Marr Show, they said, and he did it again in his three-and-a-quarter-hour interrogation by the Treasury select committee on Wednesday. I disagree. When Andrew Tyrie, chairing the pro-EU kangaroo court, remonstrated with his witness for interrupting questions, Johnson said: “I think I’ve demolished all the questions that have been asked.” I actually thought that was quite a fair self-assessment.

But that unusually long session raised a different doubt about Johnson’s succession: will he be overfamiliar in 2019? Will we be bored with him? Will he be like Gordon “Hurricane” Brown: someone who waited too long to be prime minister and who had run out of ideas when he got there?