Keir Starmer is a grownup. He is serious, capable, responsible, authoritative and realistic – or so he and Labour would like us to believe. Ever since he became leader, two years ago this month, one of his main goals has been to present himself as a much-needed political adult: repairing the damage done to the party by the supposed perpetual adolescent Jeremy Corbyn; poised to rescue the country from the naughty schoolboy Boris Johnson. From his strict suits and haircut to his no-frills speaking style and carefully researched Commons questions, Starmer has sought to come across as a sober prime minister in waiting, a reassuring figure in troubled times. He is 59, and if Labour wins the next election, he is likely to be the oldest successful candidate for prime minister since Harold Macmillan in 1959. It’s almost possible to imagine Starmer as a politician back in those more stable times. This old-fashioned, rather severe persona has sometimes been pretty effective. We are in one of those periods now, with Starmer easily dismissing Johnson’s shoddy homework in the Commons, and Labour ahead in the polls and expected to do well at next week’s local elections. With the Tories seemingly running out of talent and policy options, a Starmer government is starting to become imaginable. Yet at other times during his leadership, his “grownup” act has fallen flat – and it could easily happen again. Next to Johnson’s antics and the drama of the pandemic and Ukraine, any opposition leader would sometimes struggle to get attention. And Starmer, with his methodical, rather than intuitive, approach to strategy, his slightly yelping voice and stiff body language, is not a political natural. He is a workmanlike leader, partly because that’s his character, as the modest but growing number of Starmer biographies make clear. More importantly, his leadership style also reveals a lot about his party and our wider politics. Ever since Labour’s crushing defeats and loss of confidence in the 1980s, to be a grownup Labour leader, in the eyes of most journalists, Labour MPs and strategists, has meant moving to the right. Neil Kinnock, Tony Blair, Gordon Brown and Ed Miliband led in very different circumstances, from the highly favourable to the near-impossible. But all reacted by shedding leftwing policies and acquiring more rightwing ones, by courting conservative interests and cutting adrift Labour’s radicals. Electorally, this approach only worked for Blair: a rare talent whose tenure also coincided with a particularly weak and divided Tory party. Otherwise, many voters, after initially being intrigued, have tended to conclude that Labour leaders who offer ideologically “moderate” maturity are a bit boring, inauthentic, or not to be trusted. The same newspapers that help persuade Labour leaders to shift rightwards often then tell their readers that the party has not shifted enough. Kinnock, for example, got a good press for bashing the left in his early years as leader; but when he looked as if he might actually win an election, in 1992, the tabloids destroyed him. Yet Labour’s urge to seem grown up persists. Partly it’s sustained by the conviction that a less respectable, more leftwing party would do even worse at elections – which is why it’s so important both to New Labour veterans and Starmerites that the huge vote for Corbyn in 2017 is forgotten. Behind this conviction is another layer of pessimism: a belief that Britain, by which the Labour grownups usually mean England, is fundamentally a conservative country. In this environment, the argument goes, Labour can only exist as a significant force if it looks safe and sensible. The importance of retired voters in general elections, and the collapse since 2010 in the proportion of them choosing Labour, from about a third to about a sixth, add to the pressure on Starmer to be conventional. In today’s Britain, growing up, political maturity and the renunciation of leftwing politics seem to go together more than ever. As leader, Starmer has reinforced this connection. In his youth, he was part of a radical collective that produced Socialist Alternatives, a short-lived 1980s magazine which argued presciently that the left should pay more attention to the environment and feminism. Yet on Desert Island Discs in 2020, he mocked his days at the magazine: “We were out to change the world … I said some things that were daft.” He had become less dogmatic, he continued, “as I’ve grown up”. But the idea that radicalism is always immature and naive is itself a form of dogma. During the 1990s and 2000s, when much of the west was relatively stable and prosperous under centrist governments, this cautious view of politics was fairly easy to justify. Yet today, with the climate emergency and capitalism lurching from crisis to crisis, it is the anti-radical position that often seems unrealistic. When the climate activist group Just Stop Oil began blockading fuel depots this month, Labour called for “immediate nationwide injunctions” to halt the protests, because they “cause misery for motorists”. This stance may please some voters at the local elections, but it’s unlikely to seem wise in years to come. The same goes for Starmer’s neglect of the young left that Corbyn mobilised, which could have been Labour’s future. In our era of flux, is there a chance that Starmer’s leadership could change? In Oliver Eagleton’s persuasive new biography, The Starmer Project: A Journey to the Right, his trajectory seems set: an idealistic lawyer protecting civil liberties gradually metamorphoses into a paternalistic party leader promising voters “security”. In theory, the latter offer still has radical potential, as one of the main causes of insecurity in Britain is our version of free-market capitalism. As leader, Starmer has repeatedly said that he wants an economy which is no longer “rooted in insecurity and inequality”. Were he to become prime minister, however, the pressure to drop this goal would be considerable: many businesses have done very well out of Britain’s harsh economic model. Taking advantage of the Tories’ difficulties with some employers over Brexit, Starmer has already been trying to woo the private sector by calling Labour “the party of business”. To his admirers and lieutenants, such manoeuvres are simply grownup politics. If you want an end to Tory rule, they argue, this stern man in a suit is the person to deliver it. They may be right. But being a fully functional prime minister, like being a fully functional adult, isn’t just about professionalism and authority. It’s also about the ability to charm, communicate effectively, show empathy. We’ve yet to see those sides of him – if we ever will. Without them, a Starmer government, however welcome at first, will be hard work for him and for us. Andy Beckett is a Guardian columnist