An abiding curiosity of recent British political history is the speed at which recently loathed leaders become more palatable in light of their abysmal replacements. If Boris Johnson seemed the worst prime minister in every conceivable category, Liz Truss – perhaps her major achievement in government – found new ways to unseat him. Theresa May, considered reliably awful for most of her three-year tenure, appears a model of sanity compared to her successors. As a measure of this, the unveiling this week of a portrait of May triggered not the gag reflex of yore but something almost like warmth. My first thought, on seeing the painting, was that if I didn’t know who she was, I would totally hang that on my wall. Kudos must go to the artist, Saied Dai, who has seemingly done the impossible and imbued the former prime minister – whose greatest admirers couldn’t accuse her of having an inspirational leadership style – with an air that appears almost noble. The portrait, due to be hung in Portcullis House, combines a Bloomsbury-era vibe of sharp angles and sludgy colours with what feels like a Napoleonic cross-body positioning of May’s arm. Her expression has more depth and humour to it than any one can summon from memory. “Look at me,” she appears to be saying. “Don’t seem so terrible now, do I? Suckers.” What is particularly striking about this portrait is the ways in which it is, necessarily, at odds with May’s image at the time of her leadership. Painting former political leaders – or, unless you are Francis Bacon, painting anyone at all, perhaps – demands a measure of flattery that can manifest as enhancement or denial. One of the best recent political portraits, Kehinde Wiley’s painting of President Obama, places the former president before a backdrop of foliage, in a suit but no tie and, while straight-backed, also informally sitting in a chair. It captures perfectly Obama’s ability to be simultaneously statesmanlike and approachable, summing up his ease of manner, his casual confidence. Everything about it says, “I’ve got this.” May appears more formally, in a standing position and with a greatcoat balanced on her shoulders. You could say she is holding herself in – that the arm across her torso is less statuesque than anxious – but to me, the combination of the coat, the dangling left arm, and the air of slight amusement communicates a jauntiness a long way from her personal and political image. The artist achieves something all good portraiture must, which is, seemingly, to tell me something about the subject I didn’t already know. For a second, before I can remind myself of, say, the former home secretary’s “go home” vans or her flip-flopping around Brexit, Dai’s rendition of May, with its hints of an actual interior life, makes me think wait, did I have this person all wrong? A similar dynamic takes place, to negative effect, in Chuck Close’s weird, looming 2006 portrait of Bill Clinton, a painting that, while striving to capture the former US president’s man of the people vibe, instead gives the viewer a startling insight into what it might be like to find oneself, as so many women have, standing too close to the man. Or Paul Emsley’s out-of-focus 2013 portrait of the Duchess of Cambridge, which looks like the kind of painting you might find propped up in somebody’s driveway during a garage sale. (Although, oddly, the more you look at it, the more you start to think that Emsley inadvertently got at the terrible limbo state of the royal consort, with its blurry, empty vacancy). And while a lot of people hated Lucian Freud’s 2001 portrait of the Queen it is, in my view, the only royal portrait ever truly to get at the demands of the role. There’s an argument that, as with any kind of portraiture, written or pictorial, too full-throated an endorsement from the subject in question is the quickest indication the piece has failed. Typically, May’s response to Dai’s portrait was formulaic and bland, calling it a “huge honour,” and a “fascinating process”, and that she was “thrilled” by the finished result. She sounded, to my ears, nervous of having an opinion, of being caught saying the wrong thing about art. On the other hand, maybe she was genuinely thrilled? Impossible to know, based on experience, whether words used by May are rooted in any kind of conviction. And so we return to the easier sell of the former prime minister in illustrated form: formidably present, poised for action, deep of thought and grave of manner, sensitive to the ironies of life, vast and small. Not the leader we knew at all, in other words. But a lovely portrait. Emma Brockes is a Guardian columnist