As the UK lurches towards Brexit, one intriguing question has no satisfactory answer. Namely, from where did Arron Banks get the £8m he gave Leave.EU? Banks insists the cash is his. But the National Crime Agency has launched a criminal investigation and during an appearance on The Andrew Marr Show Banks failed to explain this mystery.

The suspicion for some – again, denied by Banks – is that the money came from Moscow. In cold war times, the Kremlin sought to influence western politics by boosting communist parties. These days, Vladimir Putin backs disruptive candidates from the far right and far left. There is covert and sometimes overt money. Plus bots, hackers and spies.

The election of Donald Trump in 2016 inspired a slew of books on Russian interference. One of the best is The Road to Unfreedom by Timothy Snyder – a brisk, conceptually convincing account of democracy’s retreat in the early years of the 21st century, and authoritarianism’s giddy rise.

Putin, according to Snyder, is the world’s leading exporter of the “politics of eternity”. Russia (or America) is an eternal victim. All politicians lie, the idea of progress an illusion, and truth unimportant. Trump, in this reading, is Putin’s willing pupil: an exponent of mythical, grudge-based politics and emotive nationalism.

Another valuable study of Russian influence is Putin’s Kleptocracy, by the late Karen Dawisha. Dawisha explains how Putin and his circle emerged from a criminal 1990s St Petersburg. They accumulated billions – money that can be spent on buying a yacht, or on more explicitly political projects, such as hacking a foreign election or running a troll factory.

In Moneyland, Oliver Bullough writes mordantly and well about the role played by the west in enabling global corruption. Typically, Russian oligarchs use London to launder their reputations. They reinvent themselves as philanthropists, hire expensive PR firms and use libel lawyers to spook investigative reporters. The result: our democracy is corroded.

Meanwhile, there have always been Brits who embraced Moscow. Paul Broda’s Scientist Spies: A Memoir of My Three Parents and the Atom Bomb explains why communism appealed to an idealistic generation shaped in the 1930s by the struggle against fascism. It’s a wonderful blend of the personal and the political, drawing on family letters and declassified MI6 files.

Broda’s British step-father was Alan Nunn May, a talented scientist. His Austrian father Berti Broda was an underground communist activist. Both worked on the UK’s atomic research programme and passed secrets to the Soviets. Nunn refused to accept KGB cash. His motivation was ideological and arguably noble: to ensure the Soviet Union had nuclear parity in a post-war world.

Ben Macintyre’s The Spy and the Traitor tells the extraordinary story of Oleg Gordievsky, KGB officer and secret MI6 agent. As a member of the KGB’s London station Gordievsky was tasked with infiltrating the British establishment. The goal was to extract information from opinion-formers: politicians, journalists and others in positions of power. The KGB had a modest network of contacts and informants. Most were unaware that the charming Soviet diplomats who bought them lunch were actually KGB spies. Gordievsky’s attempts to get real intelligence were so unsuccessful that MI6 was forced to help. It give him “chickenfeed” – real but low-grade material sent back to Moscow.

According to Macintyre, the dying USSR failed to recruit any significant British agents, but Putin’s modern espionage agencies may still try the same techniques. In autumn 2015 a Russian diplomat, Alexander Udod, invited Banks to meet Russia’s ambassador in London. The government subsequently expelled Udod for spying after the novichok case of Sergei Skripal.

• Luke Harding is the author of Collusion: How Russia Helped Trump Win the White House, published by Guardian Faber.