In an overheating hall on the banks of the Clyde, Keir Starmer leaps out of his seat into an even warmer embrace and whispers into the ear of Lorna Downie, an apprentice welder who has just delivered her first ever public speech. “Although she was feeling really nervous before, I told her she’d absolutely knocked it out of the park,” he recalls later as he heads home. “For her to do that in front of the nation’s press and all the cameras was incredible. I loved it.” Starmer has himself, of course, sometimes felt uncomfortable in the hot glare of the spotlight under which he has placed himself. But there is a similarly uneasy relationship between all this apparent empathy and decency and an image that crystallised further last week: one of a cold-eyed and ruthless Labour leader determinedly changing his party. Campaign coverage over recent days has been dominated by claims that he is “purging” leftwingers – including Diane Abbott, who was reportedly being blocked as the candidate in the Hackney seat she has represented for 37 years. He has never stated that publicly, instead sticking to the ugly formulation that “no decision has been taken” and an insistence that he was not directly involved in taking it. And, within an hour of his own speech in Greenock on Friday, he was back in front of the cameras trying to draw a line under the controversy by announcing she was “free to stand”. Abbott had been re-admitted to the parliamentary Labour party a few days earlier after a lengthy suspension for suggesting in a letter to the Observer that Jewish, Irish and Traveller people had not experienced racism in the same way that she had. Although there had been delays while conversations were had about whether this might be the time for her to retire with dignity, nothing had ever been agreed. But a briefing to the Times on Tuesday night that the veteran leftwinger would be blocked from standing in the election blew that out of the water. On his flight back to London on Friday evening, looking forward to seeing his family and having a night in his own bed for the first time in almost a week, Starmer tells me that the anonymous briefing against Abbott infuriated him: “It’s always a ‘Labour source’ when that person could have been a number of people in a number of places.” Ultimately, he concluded he didn’t want a dispute about the arcane details of the selection processes “running on for days” and distracting him from his central purpose in this campaign of addressing issues that matter a whole lot more to voters. He knew it would mean Tories and leftwingers alike would claim he had been forced into a humiliating retreat. But the sight of Starmer’s predecessor, Jeremy Corbyn, standing against the official Labour candidate in Islington North, as well as a clutch of his supporters being banned from representing the party in this election, would suggest the left is still losing the war. Starmer argues that Abbott is worth treating as an exception. “Although I disagree with some of what she says, in terms of the battles she’s been through and the terrible insults she has had to rise above, I’ve actually got more respect for Diane than she probably realises,” he says. “She was the first Black woman MP and has always had to fight for everything. She’s not like any other candidate.” Among those imposed as candidates last week were two of his closest allies in politics: Georgia Gould, the leader of the London borough of Camden, where he lives, and Chris Ward, formerly one of his closest aides. But campaign staff dismiss any suggestion that this has all been motivated by left-right infighting within the party. They point out that a number of MPs, including Nick Brown and Conor McGinn from the centre-right of the party, fell out of contention for re-election after resigning during separate investigations into unspecified complaints. Each had rejected the complaints as unfounded [see footnote]. Starmer himself doesn’t seem to have much regret about a process that has seen him establish a ratchet-like grip on who will represent the party. “This is the completion of a two-year exercise to make sure we’ve got the right people in the right places,” he says. “I don’t usually get involved in individual selections but what I did say at the beginning is that I want only the highest-quality candidates. The last few days is only a version of what’s being going on ever since, where every other weekend there’d be a row about who was being selected.” He says that, if he becomes prime minister, “we’re going to have to do really hard things, we’re going to have to do them at pace,” adding: “I need an absolutely top team, a reliable team, a team who understand the tough decisions we’re actually having to take.” The row about Abbott is not enough to be classed a proper wobble and will probably be forgotten soon enough. Even so, the messiness of the dispute has taken the shine off a positive start to the campaign for Labour before the first set-piece TV debate against Rishi Sunak on Tuesday, and Starmer is braced for Tory attacks on him personally intensifying. The oft-trailed “dossiers” on his record as a human rights lawyer or as director of public prosecutions before he became an MP are expected to start appearing in rightwing newspapers over the next few days. “They’re looking for some sort of gamechanger,” he says about the debates. “I will just try to keep it calm and measured.” Referring to the over-used comparison of Labour’s lead to a fragile “Ming vase”, he says, “having carried it around for a while now, I’m going to avoid the temptation to start juggling it.” This version of the Labour leader as “no-drama Starmer” is a deliberate contrast to the strategy being pursued by his opponent. “I see Sunak sort of flailing around trying to put any old idea on the table. He can’t fight on the Tory record of five PMs over 14 years and he can’t pay for whatever he’s proposing now, probably because he thinks he won’t have to. It looks a bit desperate.” Starmer has been doing debate rehearsals for some time now under the watchful gaze of Matthew Doyle, his head of communications. The role of Sunak has been played by Tom Webb, a policy adviser who has played a similar role in his preparations for prime minister’s questions. But the Labour leader thinks the debates won’t be like these formulaic “I-ask-he-answers” weekly jousts. Instead, he believes the “unfiltered Q&A campaign hustings with voters on the campaign”, or the press conferences where he usually goes through a long list of journalists rather than picking questions from a chosen few, are as good a preparation as anything. In some recent events, he has dispensed with written texts for speeches and now relies just on bullet points. “I feel a bit freer that way.” He has been following the court case where Trump was convicted on 34 charges last week, prompting the former president to dismiss the verdict of what he called “a rigged trial by a conflicted judge who was corrupt”. Starmer pointedly says it is important to maintain “respect” for the judicial system and rule of law, because if “you lose that, you lose everything”. As a public prosecutor, he had to take difficult decisions about sending MPs and newspaper executives for trial in the expenses and phone hacking scandals. He therefore feels a certain amount of sympathy for the judges and lawyers involved in this case, though he adds with a shake of the head that “this is such a different scale – off the charts – more the kind of thing you’d find in fictional books than real life”. Then he stiffens up again because, as with rows over Labour selections, this isn’t just about winning votes in the heat of a campaign. “At the end of the day, it’s up to the American people to choose who they want as their president,” he says. “When you’re in the depths of opposition, you can make all kinds of pronouncements, but when you’re serious about being in power you have to work with whoever other countries have as their leader. It’s part of being ready for government.” Conservatives have tried to paint him as “Sleepy Starmer”, in an echo of Trump’s attacks on Biden. But on the flight back to London, even as one of the Labour leader’s aides could be seen snoozing, mouth open in full fly-catching mode, his boss was saying he relished the pace of it all. “I’m up for this and there’s fantastic energy around this campaign. You know me, I just keep going. I’ve always done it.” Keir Starmer: The Biography, by Tom Baldwin, is published by William Collins (£25). To support the Guardian and Observer order your copy at guardianbookshop.com. Delivery charges may apply This article was amended on 2 June 2024. An earlier version incorrectly said Nick Brown and Conor McGinn had been “blocked from seeking reelection after falling foul of strict disciplinary rules”. In fact, while both MPs were suspended from the party pending the outcome of separate complaints processes, no determination of wrongdoing was made in either case as each resigned from the party in 2023 before the process was complete, criticising the quality of the investigation; McGinn had already announced some months earlier that he would not be standing again, citing health and family reasons.