A former Defence Secretary coming out for Leave isn’t exactly a daily event, and Liam Fox’s decision to do so today marks an important milestone in the rolling EU referendum campaign.  That a man who until fairly recently had charge of Britain’s armed forces believes that Brexit is in our national interest is a sign of the times.  Fox is still a player in the Party – performing creditably in ConservativeHome’s monthly future leader survey.  He has energy, brains, eloquence and uncomplicated Thatcherite beliefs.  This site welcomes him to the fight.

Fox’s decision to declare ratchets up the pressure on others to do so, and so we turn to another prominent Tory who isn’t a Minister.  The Mail on Sunday today follows up a well-sourced Daily Telegraph story yesterday – from “senior sources close to the Prime Minister” – claiming that David Cameron is considering making Boris Johnson Foreign Secretary.  What follows in this article is an interpretation of such a move that may be wide of the mark, but is plausible enough to be worth an airing.

The place to start is with the fact that Cameron and George Osborne are a team, and that the former will do nothing to harm the succession prospects of the latter.  So if the Prime Minister is indeed mulling appointing the Mayor of London to a great office of state – one scarcely exceeded in seniority by that which Osborne himself currently holds – the Chancellor must have a reason for wanting to see such a development.  Downing Street’s briefing to the Telegraph will thus have had the Treasury’s blessing.  And it isn’t all that hard to see what the explanation might be.

Osborne is fixed on becoming the next Party leader and Prime Minister.  This cannot be achieved without the referendum returning a Remain verdict.  Were Boris, with his capacity to reach-the-voters-who-other-politicians-can’t-reach, to come out for Leave, the Chancellor’s aim would become more difficult to achieve.  But were the Mayor, by contrast, to plump for Remain, he would effectively be neutralised – thus helping to keep the Remain campaign and Osborne’s ambitions on track.  A rough timetable might be as follows.

Boris’s term as Mayor ends in May, and this winner of the biggest personal electoral mandate in Britain cannot be left to languish outside the government.  Cameron strikes his deal at the European Council meeting which ends on February 19.  There is a snap reshuffle over the weekend.  Boris goes to the Foreign Office.  Philip Hammond perhaps becomes Leader of the House, replacing Chris Grayling – who, as a backer of Leave, has presumably resigned if Cameron does not allow Ministers the freedom for which Graham Brady rightly argues in today’s Sunday Telegraph.

Such a decision by Cameron would pile pressure on the other Leave sympathisers in the Cabinet – Michael Gove, Theresa Villiers, Priti Patel, presumably John Whittingdale, and perhaps Theresa May – to toe the line.  Iain Duncan Smith will surely have none of it, and represents a headache for Number Ten (though the Work and Pensions Secretary has, as a former Party leader, a natural sympathy for the Prime Minister’s plight).  Boris thus enters the Cabinet fully signed up to Cameron and Osborne’s position.

The referendum duly returns a Remain vote in the summer or perhaps in September.  Cameron leaves Downing Street almost immediately, thus allowing Osborne the opportunity to replace him while the latter’s stock is high.  In effect, therefore, the Mayor is disarmed not only as a referendum problem but also as a leadership rival. The Chancellor has him pronged on a Morton’s fork.  If he refuses the offer, this is further evidence, Team Osborne would then argue, that he is not a team player.  But if he accepts, he is boosting Osborne’s leadership prospects at the expense of his own.

For although the Foreign Office is indeed a great department of state, it is one that a determined Prime Minister can now effectively sideline.  This is exactly what Tony Blair did to it after the departure of Robin Cook.  Old Demon Eyes left that department diminished, and it has been restored to its previous standing only during William Hague’s tenure as Foreign Secretary.  It is Cameron and Osborne, after all, who are running this renegotiation – not Hammond.  Boris’s fate would be to clock up the air miles while the Chancellor digs in at Westminster.

It may be significant that the idea of sending the Mayor to the Foreign Office was floated by Daniel Finkelstein in the Times earlier this week.  Lord Finkelstein dislikes being seen as a conduit for the views of his old friend, and there is indeed far more to his regular column than that.  Perhaps inspiration in this case is working the other way round, or the timing of the column was a mere coincidence.  But its appearance looks rather like one of those letters to the same paper which claim sight of the first cuckoo of spring – that’s to say, a portent of changing weather (if not climate).

As I say, my reading of what seems to have been a very well-sourced story may be wrong.  Team Osborne may conclude that giving Boris such a big leg up would mean too big a risk: few are more skilled than the Mayor at using vantage to push his own prospects.  Perhaps it would be safer, from the Chancellor’s point of view, for Amber Rudd to be sent to King Charles Street and Boris to be offered her Environment post.  After all, she has just represented Britain at a major negotiation, and building her up might help to knock Theresa May, another potential Osborne rival, down.

Maybe the apparent inducement of the Foreign Office is a feint – a mere dangling before the Mayor of goodies to come if he behaves himself.  Perhaps there will be no deal in February and no referendum next year.  But what is certain is that the Mayor has some very serious thinking to do this yuletide, as he plops his feet up near a roaring fire, and gropes for his beloved volume of The Odyssey with one ham-like hand while scooping up a stackful of After Eights with the other.

His natural inclination will be to go for Remain – since its cause is more likely to win out than Leave’s.  If he goes for it, he will find it hard not to take Osborne’s bait, and consign himself to marginalisation.  But if he doesn’t, he will have committed himself to what, on balance, is still likely to be the losing side – and a road to potential oblivion.  “Will you walk into my parlor?” said the spider to the fly;/ “’Tis the prettiest little parlor that ever you did spy. /The way into my parlor is up a winding stair,/ And I have many pretty things to show when you are there.”  Merry Christmas, Boris!