One Thursday night in April 2016, a young Lib Dem election candidate slipped on his finest grey suit and travelled to north London to meet voters at a 'hustings' in Barnet.

Among the political hot potatoes chucked his way during the ensuing Q&A session was the thorny topic of anti-Semitism.

Specifically: some Jewish residents of the borough, which is home to several large synagogues, voiced concern about mood music emanating from the Labour Party, which had recently elected Jeremy Corbyn as leader. They complained of feeling unsafe on the streets and spoke of an uptick in anti-Jewish hate-crimes.

The Lib Dem candidate was a charismatic chap and offered a pitch-perfect response. Spreading his arms wide, he declared himself to not only be a proud Jew, but also an enthusiastic Zionist.

A vote for his party would, he insisted, represent 'support for liberalism, support for Israel and support for Judaism'.

That candidate's name was Zack Polanski. Back then, he was a jobbing 'life-coach, actor, corporate-trainer' and some-time hypnotherapist who had changed his name via deed poll. He was born David Paulden, but wanted to reclaim his family's Jewish surname - and distance himself from his stepfather, who was also named David.

After developing a sudden interest in politics a couple of years earlier, he'd decided to join the Lib Dems. He was now seeking a £63,000-a-year seat on the London Assembly. Aged 32, it would have been his first proper, full-time, salaried job.

Polanski was regarded as being on the party's 'soft-Right' wing, according to a colleague from that period. At an autumn party conference, Polanski had given a speech declaring: 'I consider the Liberal Democrats as family.'

A few months later, the Lib Dem Voice magazine dubbed him one of its 'stars of 2015'.

'We've had the benefit of him seemingly landing from space in our party with boundless energy AND efficiency, a rare combination in LD circles,' read the citation. 'He appears ambitious, but with a true liberal soul.'

That, of course, was then. But families can fall out.

After failing to win that London Assembly seat, Polanski applied for a parliamentary one, in Richmond Park. When the local party chose someone else, this 'true liberal' threw a public tantrum, complaining on Facebook that 'there's no feedback given and no appeals process. I'm pretty gutted'.

Not long afterwards, he defected to the Greens.

The party promptly found him a berth in the Assembly. He became deputy party leader in 2022 and in 2024 was elevated to leader.

What happened next represents one of the most screeching (and critics might argue cynical) U-turns in modern political history.

Polanski no longer appears on the stump offering 'support for Israel and support for Judaism'. Instead, he takes the exact opposite approach. Obsessional opposition to Israel, plus grotesque anti-Semitism, have become the party's hallmark.

Take, for example, the Greens' roster of candidates at next week's local elections. Two were arrested this week on suspicion of stirring up racial hatred via social media posts.

One, Saiqa Ali, who is standing in Streatham, shared an image of a fighter from proscribed terrorist organisation Hamas with the caption: 'Resistance is freedom'.

The other, Sabine Mairey, standing in Clapham, posted a picture of a man holding a placard that reads 'ramming a synagogue isn't anti-Semitism, it's revenge'.

And yesterday, this paper revealed Lambeth candidate Mark Bittlestone, who teaches history to sixth-formers at a south London school, has reposted material suggesting the October 7 atrocities were a covert 'false flag' attack and calling Israel a 'colony of inbreds, rapists and thieves'.

Polanski can hardly have been unaware of Ali and Mairey's vile remarks: they'd been reported to the party weeks ago. But the Greens had failed to boot them out. On the day their collars were felt, he was forced to deny well-sourced reports that he'd been due to campaign with them.

To be fair, anti-Semitic cranks are hard to avoid in the party. Once a haven for yoghurt-knitting environmentalists, it has, under Polanski, become the natural home of hard-Left Corbynistas who either became disillusioned with or were booted out of Labour by Sir Keir Starmer. They have helped membership to swell from 68,000 to roughly 225,000 in the past six months.

This tribe endorses pseudo- Marxist economic policies on everything from taxation, to border control (they want to give illegal immigrants full amnesty plus a free house and wage with no work requirements), to abolishing the monarchy and legalising heroin, crack cocaine, and the date-rape drug GHB. But its real obsession is the Middle East. Or more particularly opposition to Israel, the world's only Jewish state.

This week, Polanski's deputy, a Muslim social media influencer named Mothin Ali, was caught telling some of the few members who have actually been disciplined by the Greens for anti-Semitism that they were being unfairly treated and should sue their own party.

'What we need to do is we need to get some serious legal advice. We need to start with some class action,' he said, in a leaked recording. Note the use of the word 'we' to describe people who have used social media to foster hatred.

Ali, who is close to Polanski, has serious form. He used TikTok on the day of the October 7 attacks to argue that people should 'support the right of indigenous people to fight back'.

On the night he was elected as a local councillor in Leeds in 2024, he stood in front of a Palestinian flag and declared the victory 'a win for the people of Gaza', before shouting 'Allahu Akbar!' ('God is the greatest').

Polanski rarely, if ever, speaks out against these and other cranks in his party. In fact, he actively encourages them, usually via his own inflammatory social media posts. He leads from the front.

A few weeks back, he used X to play down concerns that heated political discourse around Gaza (particularly in Green circles) were leading to an increase in anti-Semitic attacks in the UK.

He claimed the Jewish community's rising fears might reflect a mere 'perception of unsafety' and not 'actual unsafety'.

Then came Wednesday's terror attack on Golders Green.

Polanski's response? To share a reprehensible and inflammatory post criticising the police who arrested the suspected perpetrator of the attack for 'repeatedly and violently kicking' him.

Among those appalled by that remark was Mike Tapp, a Home Office minister, who said he was 'disgusted that anyone with this view is leading any political party'. The Jewish Labour movement called it 'shocking'.

Met Police chief Mark Rowley wrote to Polanski saying the post was 'inaccurate and misinformed', and was contributing to the 'rising tensions we are seeing in society' - comments which yesterday prompted an apology from the Greens leader.

But stirring up tension via inflammatory online posts isn't an accident. It's a deliberate tactic: one of the central features - perhaps the central feature - of Polanski's political modus operandi.

To understand this point, one must think of him as a sort of hard-Left version of Donald Trump (whose extreme egotism and casual disregard for the truth he almost certainly shares).

Obsessed with online posturing, Polanski spends huge portions of his time on platforms such as X and Bluesky (a woke equivalent of Trump's Truth Social) trying to pick fights with people - the more high-profile the better - then weaponising the controversy. 'To understand Zack, you need to realise that he's not a traditional politician,' one former Lib Dem colleague says. 'He's certainly not in the game because of his beliefs, which seem to change all the time. I'd also be very surprised indeed if he wants to end up actually running anything. It's all about clout and self-promotion. Arguments get people clicking, which brings him attention and therefore votes.

'Politically, he's a huckster. In terms of his interests, he's basically a full-time content creator.' On one level, this schtick has been quite successful. Currently sitting at between 15 and 20 per cent in the polls, Polanski's Greens won a signal victory at the recent Gordon and Denton by-election, thanks largely to pro-Palestinian sentiment among the Muslim community. They will doubtless do very well indeed next Thursday.

On another, it has undoubtedly degraded the national discourse and, as Mr Rowley rightly said, is inflaming social tensions.

A case in point was detailed by The Economist, which analysed Polanski's activity on Bluesky. He's visited the site every day in the past year, the magazine noted, making nearly 35,000 visits. To put that another way, this 43-year-old man uses the site, on average, nearly 100 times every 24 hours.

'Mr Polanski has a habit of searching for his own name, a practice known as 'ego surfing',' its report added, revealing that a third of posts the Green leader has 'liked' on the platform include the phrase 'Zack Polanski'. He tends to be 'thin-skinned and hostile towards journalists and other critics', particularly female ones.

After the Guardian columnist Marina Hyde wrote a mildly critical article about him, he 'liked' at least 20 posts critical of her, including one saying: 'Marina Hyde is a total t**t.'

In October, he liked a post which described the Guardian's chief sports writer as 'a smug sanctimonious c**t'. In November, he endorsed a misogynistic post dubbing Sophy Ridge of Sky News 'a sneering d***head' for asking Polanski about his party's policies during an interview.

If one were to psycho-analyse Zack Polanski's addiction to drama, it can perhaps be said to stretch back to his childhood.

'As a child he loved dancing, he was constantly reading,' his younger half-brother Ben once told the BBC. 'Outgoing, talkative, confident… If you knew him as a kid you could see exactly how he became who he is today.'

Born in Salford in 1982, Polanski last year told the Guardian that he was the product of an impeccably working-class family, with Jewish parents, who divorced when he was young. 'His mum is an actor, his dad works in a DIY shop,' read a hagiographic profile which quoted him delivering a light-hearted dig at Keir Starmer: 'I'm not the son of a tool-maker, I'm the son of a tool-seller.'

It's a nice story. But the truth is considerably less gritty. Polanski's family were impeccably middle-class. Father Philip in 1984 set up Beronsand Limited, which lists its business as 'buying and selling of real estate'. By the time Zack was a teenager it was listing a bank balance in the tens of thousands of pounds, plus interests in a string of investment properties

in Wythenshawe, Greater Manchester, including three homes next door to each other. Mum Ava continues to work in the entertainment industry.

While the family weren't super-wealthy, they could afford a private education for everyone.

Zack went to Stockport Grammar (albeit on a scholarship), where fees are now £19,000 a year, but left after GCSEs (he claims he was bullied due to his homosexuality after peers saw him kissing 'a young Muslim man named Jihad when I was 14') and attended a local sixth-form college where he developed a love of the spotlight.

After studying drama in Aberystwyth, he spent his 20s working in community theatre, with stints as a rep for PGL, the children's holiday firm, and as a nightclub bouncer. By 2013, Polanski was also earning a shilling as a hypnotherapist, in a Harley Street clinic.

Then came his first, and perhaps still most notorious, PR stunt: via a Sun newspaper article in which he claimed to be able to increase the size of women's breasts, via the power of the mind.

When the article resurfaced, around the time of his elevation to the leadership of the Green Party, Polanski repeatedly claimed to be the victim of an underhand tabloid sting, saying he had been 'mis-represented' in the piece and had made a public apology 'a day later'.

That claim was, however, recently revealed to be completely untrue: the BBC discovered an interview Polanski had given to BBC Radio Humberside, a week after the Sun piece appeared, describing it as 'a successful project' in which his patient's bust 'grew by four inches' and boasting about hypnotherapy providing 'anecdotal evidence at least of a growth in breast size'.

Two years later, Polanski joined the Lib Dems.

A casual disregard for the truth became apparent in his first major political gig, speaking to the party's 2015 autumn conference in Bournemouth. Dressed in a dark suit - one attendee recalls that he resembled Kenny Craig, the hypnotist in Little Britain whose punchline is 'look into my eyes' - he performed a series of song routines with a gospel choir, and delivered a speech about his burgeoning political career.

At one point, he said: 'I phoned over 2,000 new members personally and asked them why they had joined the party.'

Says the attendee: 'I remember watching that and rolling my eyes. It was plainly untrue. It was simply impossible.'

Plenty of politicians tell tall tales, the attendee adds, 'but while that one was relatively harmless, it marked him out, to me as a show-pony who couldn't be trusted. A few months later, he went off to the Greens.'

Today, the Lib Dems regard Polanski's defection as a lucky escape, watching aghast as the social media controversialist who once urged voters to provide 'support for Israel and support for Judaism' has turned the Greens into a sewer of anti-Semitism.

Continued online posturing will, for the time being, win votes. And in the shallow world of social media, the ever-changing nature of Polanski's personal narrative has so far been ignored.

But his brand of combative celebrity politics is also stirring up dark forces, and no one quite knows how this increasingly troubling tale will end.

Additional reporting: Tom Kelly