“Republic of Lies – American conspiracy theorists and their surprising rise to power”, by Anna Merlan. Penguin/Random House

My favourite of the many and varied conspiracy theorists cited in Anna Merlan's Cook's tour of the wild and wacky, has to be our own David Icke. This former BBC sports reporter has a vast and loyal following for what must be the most high concept conspiracy theory since Satanism.

The world is run, he claims, by a tightly-knit group of “reptilian entities” - the Queen Mother was one – who've been collaborating with Rothschild Jewish bankers and climate scientists, to set up a global green dictatorship and enslave humanity. He's published 20 books, and made lucrative career travelling the world delivering lectures on his bizarre passion.

Ickism is so bonkers you wonder how anyone could believe it. But his is a portmanteau conspiracy theory, drawing together a raft of diverse conspiracies, already widespread on the internet, which Merlan explores in this entertaining taxonomy if toxic ideas. Anti-vaxxers, Ufologists, antisemites, evangelicals, Deep State truthers, climate change and holocaust deniers can all find confirmation in his gnomic utterances. Icke is a one-stop shop for the paranoid and the mildly deranged.

The Protocols of the Elders of Zion, a fabricated blueprint for Jewish world-domination that dates from late 19th Century Russia, gets mashed with other conspiracies involving the Illuminati, the Bilderberg Group, the Club of Rome, the CIA, Mi6, and curiously, the London School of Economics. These are all controlled by an entity called the Babylonian Brotherhood, who work on behalf of the lizards in a parallel dimension.

He is not alone in making a good living out of conspiracy. Alex Jones, the shouty vlogger of the alt right website Infowars, doesn't buy the lizards, but he's signed up to most of the rest of the paranoid agenda. His source conspiracy is the Deep State – a bureaucratic/corporate entity at the heart of government, which is secretly controlling our affairs on behalf of remote banking elites. 9/11 was a staged event, a “false flag”. School shootings, like Sandy Hook, are also faked by the government, Jones supporters believe, in order to discredit the Second Amendment and force Americans to give up their guns. Hillary Clinton is a murderer who rapes children. Oh and here's a really great range of health products for you and your family...

You could be forgiven for thinking that conspiracy theories are really part of the entertainment industry, the product of internet hucksters and snake oil salesmen. But of course they’re no joke. A lot of people believe that government is a conspiracy against the people – we find echoes of it among Brexit supporters in the UK.

The anti-vaxxer theory that the MMR vaccine causes autism, launched by discredited medical researcher, Andrew Wakefield, in a Lancet article in1998, has led to the spread of a potentially deadly disease: measles. One of Alex Jones's pet conspiracy theories, that Hillary Clinton was at the centre of a paedophile network that operated from a chain of pizza restaurants, led to one “truther" turning up at a Washington branch of Planet Ping Pong armed with automatic weapons.

Most of us associate conspiracy with the far right, with white supremacists, the Ku Klux Klan and Russian trolls. But conspiracy theories, according to Maran, are deeply rooted in the African American community, and not just among the Nation of Islam extremists. She quotes Barack Obama's own one-time preacher, Reverend Jeremiah Wright, accusing the government of “inventing the HIV virus as a means of genocide against people of color”. She says that rap music, “the black CNN”, perpetuates many racial conspiracies, including claims that the flu vaccine is is a means of controlling black people.

Historically, antisemitic and Deep State conspiracies have undoubtedly been the preserve of the right. But Maran, a socialist feminist, has the intellectual honesty to include the liberal left in her demonology of the paranoid. Indeed, she compares the CNN presenter, Rachel Maddow, and the prolific British blogger, Seth Abram, to conspiracists like Alex Jones, in their enthusiasm to believe that Donald Trump was a Russian agent. “The Russia frenzy”, she writes, “produced rhetoric that replicated that on the conspiratorial far right, with conspiracy stars to espouse it”.

Merlan thinks that these ideas fulfil a very deep need among many of us to believe that our lives are controlled by shadowy elites. The internet has dragged these paranoid delusions into the public realm. “Social media, she says.” has created the world's most efficient vehicle of delivery of conspiracy theories...a lightning fast way to spread blame, doubt, enmity and politically expedient rumour-mongering.”.

That is true. Though I'm not entirely convinced that conspiracists like Alex Jones have “risen to power” as the title of her book claims. She concludes with an appeal to “better education in science and media literacy” along with a fairer society. But I think there is a simpler explanation for the persistence of weird theories. As the marketing pundit, Seth Godin, puts it, “facts are boring”.