Could a general of the SBU, the security service of Ukraine, really have helped Russia take the city of Kherson? Could a colonel have tipped off the Russians as to where the Ukrainians had lain mines north of Crimea?

The Ukrainian government certainly appears to believe that fifth columnists within the SBU have been Moscow’s secret weapon in this war – this week Volodymyr Zelensky fired the head of the agency (and his childhood friend) Ivan Bakanov, along with the country’s prosecutor general, Iryna Venediktova. A total of 651 alleged treason and collaboration cases have now been opened against prosecutorial and law enforcement officials, and more than 60 officials from Bakanov and Venediktova’s agencies have been accused of working against Ukraine in Russian-occupied territories.

Zelenksy’s purge of the SBU did not come out of the blue. For years there have been deep-seated concerns about the agency, which has been dogged with allegations of corruption, abuses of power and Russian penetration.

Back in 2020, I asked a Ukrainian think tanker what he thought the biggest threat to his country was, expecting him to say Russia. Instead, he immediately answered, ‘the SBU, because only we Ukrainians can break our own revolution.’

Formed out of the Ukrainian division of the Soviet KGB in 1991, the SBU managed to avoid serious reform for decades. It remains a huge agency with more than 35,000 staff, close to the size of the US Federal Bureau of Investigation and eight times as big as MI5.

Since the 2014 ‘Revolution of Dignity’ there has been progress in bringing greater transparency, professionalism and honesty to the agency though. One US intelligence officer was fulsome in praising the work done by a unit he worked with from 2019 to 2021, before pausing and reluctantly adding ‘but there are still some people and whole departments that really wouldn’t be out of place in the KGB.’

From my own experiences, I have met tremendously impressive SBU officers, genuinely committed not just to defending their country from foreign threats and domestic challenges, but doing so in a way that is transparent and follows the law. Yet at the same time – despite the fact that I have been blacklisted by the Kremlin – the closest I have come to being arrested by any security agency in the region was by a bunch of thuggish SBU heavies who were looking either for a payoff or some fun at a foreigner’s expense.

The fear that the SBU could be a serious threat to genuine political reform helps explain why, in 2019, Zelensky appointed as the SBU’s director not a career intelligence professional but his childhood friend and the manager of his election campaign headquarters.

It was controversial at the time, but reflected the new president’s clear mistrust of the existing power structures inside the agency. He thought an outsider like Bakanov had the best chance of being able to bring about real change. Bakanov has had successes to be sure, helped by considerable western assistance. While the British, American and other intelligence communities focused on practical capacity-building, EUAM, the EU Advisory Mission for Civilian Security Sector Reform, pushed for proper legal oversight.

This led to what one American intelligence veteran called the ‘two SBUs.’ There were departments in which predominantly younger officers had embraced the reforms, and others where cabals of old-style spooks resolutely resisted it. Sometimes it was simply because they were corrupt and had no intention of trimming their lifestyles to match their salaries. General Andriy Naumov, for example, fled Ukraine just before the Russian invasion and was subsequently arrested in Serbia, in the company of an alleged German smuggler, and in possession of a collection of emeralds and more than £600,000 in dollars and euros. He was the head of the SBU’s internal affairs department.

In other cases, though, there has been a perverse resistance to change from conservatives who feel that all this new-fangled transparency and accountability gets in the way of defending Ukraine from Russian espionage and subversion. This is not a simple story of corrupt officers suborned by Russia pitted against liberals and reformists, fighting for the soul of the SBU.

Of course, many corrupt officers were targets for Moscow’s recruitment. However, one of the many reasons why Russia’s initial attack in Ukraine failed was that Putin believed there was a trove of Ukrainians, including corrupt officers paid by Moscow, ready to welcome the invasion. But while many officials, oligarchs and officers gladly took Russian money, when the invasion arrived they had no real intention of helping Putin’s forces.

In fact, many of the old hands inside the SBU resisting reform consider themselves true loyalists. Before the war transfigured Zelensky into a cross between Churchill and Che Guevara, nationalists regarded him as weak, untrustworthy, and possibly even unpatriotic – including many within the SBU.

A US officer, for example, recounted a bibulous retirement party for one SBU veteran at which the mere mention of the president’s name was enough to trigger a torrent of vitriolic (and anti-Semitic) abuse from what he described as ‘real hard-core patriots,’ one of whom has since been killed running weapons to guerrillas behind Russian lines.

These hard-core elements of the agency arguably meant that Bakanov was bound to fail. And now that Ukraine is in a full-scale war, any talk of reform of the SBU has been shelved indefinitely.

The agency will continue to be one of the fiercest and most dedicated guarantors of Ukraine’s sovereignty and also one of the most serious potential threats to the vision of a democratic, law-based nation that was at the heart of the ‘Revolution of Dignity.’ Of such paradoxes and complexities, after all, modern Ukraine is made.