On a Friday afternoon in April 2022, Mark MacGann sat alone at the kitchen table in his farmhouse in the south of France and wrote a LinkedIn message to a journalist he had never met. He had been listening to podcasts about Russian oligarchs and their enablers in London — lawyers, politicians, lobbyists, accountants — and felt he had something to contribute. He did not say much, only that he had “lived experience” to share and wondered if the journalist — me — might take a call.

MacGann had spent the previous two decades in the upper echelons of corporate power, brokering deals and political influence from Moscow to Brussels and New York. He had advised on Martha Stewart’s insider trading case and helped Uber bulldoze its way through regulation, as the company’s chief lobbyist in Europe, the Middle East and Africa. At Veon, the telecommunications conglomerate with operations in post-Soviet markets, he had been dubbed “foreign minister” by a principal shareholder, the Russian oligarch Petr Aven.

Veon paid MacGann a salary of €900,000 and a bonus of €900,000 to smooth its path into international markets. “I enjoy the things money brings,” MacGann told me. But now he was alone in his house, once part of a viscount’s estate, with two boxer dogs and a cache of files that he claimed, if released, would raise new questions about how Veon — and Aven — operated under the scrutiny of a US-imposed reform programme.