Were Theresa May’s negotiation plan a Sherlock Holmes story, the great detective might tell Dr Watson that, as so often, the answer to a mystery which vexes so many lies right beneath our noses.

“Never neglect the obvious, my dear Watson.”

“What on earth do you mean, Holmes?”

“I mean this: ask yourself a question right at the start.  Has the Prime Minister ever conducted an EU-wide negotiation before?”

“I don’t understand you, Holmes.”

“My dear Watson, were my investigations dependent on your understanding they would, alas, have had fewer successful resolutions for you to bring to the attention of the world.  I refer of course to the notorious case of the EU Police and Criminal Justice measures.”

“You are unjust to me, Holmes.  I remember the story perfectly well.  The Prime Minister, when Home Secretary, opted out of 133 EU criminal justice measures –

” – And opted back into 35 of them, Watson, including the European Arrest Warrant.”

“I confess, Holmes, that your memory has the advantage of me.  But, even so, I fail to see the connection between these earlier proceedings and today’s Brexit negotiations.”

“Do you now?  Well, let us consider what we know about the Prime Minister.  We know that she previously served as Home Secretary – indeed, as the longest-serving holder of that post since the war.  We also know that many of her immediate circle of advisers also worked at the Home Office.  And we know, too, from the tale of the great Hinkley Point stand-off that she tends to view events through a Home Office lens.  So why should not her earlier negotiation, in which she invested so much personal and political capital, now serve as a model for her to draw on?”

“I don’t follow, Holmes.”

“Do you not, Watson?  Then let me draw to your attention the estimable figure of Greg Clark, now Secretary of State for Business, Energy and –  ah, yes – Industrial Strategy.  You saw Dr Clark’s appearance on The Andrew Marr Show yesterday, did you not?”

“Alas no, Holmes.  Our televison is rendered inoperable by your having adorned it with a patriotic E. R. done in bullet-pocks.”

“Then let me enlighten you.  The Business Secretary has been compelled to show part of the Government’s negotiating hand.  More, and he would have revealed a greater part of it.    Less, and he would have been pursued by incessant Urgent Questions in the Commons.  At any rate, he said that his objective is to achieve a Nissan deal ‘without tariffs and without bureaucratic impediments’.  The reference to tariffs is plan enough.  But what do ‘bureaucratic impediments’ suggest to you, Watson?

“I have it, Holmes!  They are other obstacles to trade!  By stating that he wishes to avoid such impediments, Dr Clark is indicating that he wishes – and therefore the Prime Minister also wishes – Britain to remain a member of the Customs Union!”

“On the mark, my dear Watson, but not in the gold.  You see, he also said that he was able ‘to reassure Nissan – and other manufacturers – that that is the way we are going to approach it’.  You grasp the significance of the reference?

“I confess that I find myself at a loss, my dear Holmes.”

“Sectoral deals, Watson!  ‘Other manufacturers’, don’t you see?  Cars may get one sort of deal.  Financial services, say, another.  For one, we may be part of the Customs Union.  For another, we may not.  For you see, Watson, if one has first opted-out of all EU arrangements, one may then be free to opt back into them, on a case by case basis. Precisely as was the case in relation to those Criminal Justice measures.

“Holmes, you astound me!”

“We may see here, Watson, an outline of the “bespoke deal” to which the Prime Minister’s spokesman referred during her recent visit to Brussels earlier this month.  The Chancellor of the Exchequer used the very same phrase when before the Treasury Select Committee last week.  You will find cuttings from the Morning Post relating to each transfixed by a jack-knife in the very centre of our wooden mantelpiece.  The implications for immigration policy are clear, are they not?”

“Not, I confess, to me, Holmes.”

“Why, Watson, it’s as clear as daylight.  If one is a member of the Single Market, then the four freedoms are indivisible, and migration numbers cannot be adequately controlled.”

“Germany, Holmes? Lichtenstein?

“The German restrictions are limited to welfare payments, Watson.  Our referendum result suggests that the British people want a reduction in numbers, whether those who enter are able to work or not.  Lichtenstein need not detain us.  Were such an offer available to us within the EU framework, it would have been made to David Cameron.  And we might not now be poised to exit the Union.”

“So how does this bespoke model apply to migration?”

“Well, Watson, we might conjecture that Britain first opts out of the Single Market as well as the EU…and then opts back into freedom of movement for higher-paid EU workers – but for those migrants only.  You will noted that Migration Watch has floated a work permit scheme.  You may also have seen that British Future has suggested quotas “after public hearings with employers and local communities”.  The article is in today’s Financial Times.  You will find it secreted in the toe end of my persian slipper.  But there is another dimension to the Prime Minister’s plan.”

“Name it, Holmes.”

“Why, do you not see it, my dear Watson?  Does it not occur to you that, if the Prime Minister’s negotiating approach is sectoral, she has found a backdoor means of implementing her “real industrial strategy”?  Talk about picking winners!  Businesses will be beating a way to her door to demand passporting, research grants, customs union access, special favours.  Brexit and the industrial strategy turn out not to be opposites, but complementary!

“Most ingenious, Holmes.  But isn’t there a flaw in the Prime Minister’s brilliant scheme?”

“Name it, Watson.”

“Well, Holmes, simply that our EU interlocutors may tell her to get lost.”

“Ah, there you have me.  These are deep waters, and one does well simply to keep afloat.  I merely point a way.  It is for others to determine whether it is passable.  And now, my dear Watson, we may turn our thoughts to more pleasant channels. I have a box for Les Huguenots.  Have you heard the Des Reszkes?  Might I trouble you then to be ready in half an hour, and we can stop at Marcinis for a little dinner on the way…”