How much does the British political world really know about Boris Johnson? It certainly thinks that it knows a lot. After all, Johnson has been around for a long time. He has always courted publicity. He possesses a mega-wattage personality. Many will feel that they know too much about him rather than too little.

But there is a danger that politics may not be keeping up with the way he is evolving as prime minister. On the right, Johnson is still the conquering hero. He won the Brexit battle, trounced the liberal establishment and has led the Conservatives back to a level of power they have not known for 30 years. On the left, Johnson is the villain of the era. He has hitched his ambition to a rightwing nationalist deregulatory project, and he is a Trump admirer who does not care what gets in his way, or who suffers, as long as he wins.

Pinning down the real Johnson is trickier than these caricatures suggest. Johnson may indeed have won the referendum and led the Tories to election victory on the “ get Brexit done” platform. But he is more complex than that. He was a politically liberal mayor of London, he loses no opportunity to identify with the Tories’ one-nation reformist tradition, and he talks the talk about post-austerity public spending. In fact, Johnson may be better understood if he is treated as the unknown prime minister.

Johnson must satisfy new Tory voters by unifying NHS and social care systems Read more

Underpinning all this – and it feels increasingly important – Johnson has behaved with far more political discipline and care ever since he moved into Downing Street than he appeared to do in the past. This may not last. It may be an illusion. He may be knocked off course. The discipline may be at the service of an undeserving purpose. But it implies a degree of calculation that requires more recognition than it sometimes gets.

Note in particular that, thus far, this discipline has been a feature of both of Johnson’s two periods in Downing Street, not of one rather than the other. In the first phase, after succeeding Theresa May in the last parliament, everything was subordinated to winning on Brexit and to fighting an early election. Discipline made absolute sense in such circumstances. It was massively rewarded at the polls.

Yet now those constraints no longer apply. Brexit is settled. The election is well won. But the discipline has not been binned. Johnson’s visit to Sedgefield in December and his recognition that former Labour voters expect him to deliver for them were early signs that he is working to a plan. When he told the cabinet that he is a “Brexity Hezza”, Johnson signalled that the redressing of regional imbalances in the manner of Michael Heseltine could be at the heart of the new political era.

Discipline has been a marked feature of Johnson’s handling of the current Iranian crisis. Two aspects stand out. The first is the moderation of the public British response. This has stuck closer to the stabilising instincts of Germany and France than to the intemperate ones of the US. The second, though much criticised by his opponents, is Johnson’s reluctance to grandstand the Iranian issue in the presidential manner that most modern prime ministers have adopted. Both of these choices may be tactical – not least because of the Nazanin Zaghari-Ratcliffe case, for which many blame him – but that does not make them either insignificant or unwelcome.

A similar restraint can also be discerned in Johnson’s handling of his signature issue of Europe. He is determined to treat Brexit as a done deal. The Brexit department is to close. The word itself is to be outlawed from Whitehall. But Johnson knows that Brexit is an oceanic process. It can’t be wished out of existence.

What matters to him is to change the subject. That is why he is determined to do a trade deal that protects supply chains and to move Brexit off the agenda. No-deal preparations – which would have perpetuated the Brexit conflict – have been stood down, it was reported this week. Europeans are being hugged close, as Iran illustrates. Ursula von der Leyen was feted at Downing Street on Wednesday.

How significant is all of this for the longer term? This is only the start of whatever process is evolving. I am not suggesting that Johnson is either sympathetic or visionary. But if you listen to Johnson’s words, and examine the decisions that he has made so far, his purpose is hiding in plain sight. He is planning to move his party towards the centre, by casting it as the supporter and enabler of middle-Britain voters who want spending on the NHS, social care and the climate emergency. Polling for the thinktank Bright Blue this week shows Johnson has a job on his hands to clinch that deal.

At the close of Shakespeare’s Henry IV, as Prince Hal is about to be crowned king, he stuns his former drinking companion Sir John Falstaff by telling him: “Presume not that I am the thing I was./ For God doth know, so shall the world perceive,/ That I have turned away my former self.”

In Johnson’s case it is hard to be sure whether he has turned his former self away. And these are very early days in what may be a very long premiership. But Johnson does not have to turn all the way from Hal to Henry to show that there are likely to be more shades of grey in his prime ministership than some have yet grasped.

This feels very much like Week Zero in the real Johnson premiership. As it gets under way, there is a strong case for wondering how much of Johnson’s past is actually a reliable guide to the present. Some embryonic things about his premiership, which may not last, suggest that it may be more formidable, and certainly more interesting, than many have supposed. In the light of one of the most radical electoral changes in modern history last month and the paramount need to understand it properly, it might be more useful to dispense with too many prior assumptions and start instead with a blank page.

• Martin Kettle is a Guardian columnist