Few could have expected that the year’s biggest protest symbol would be the humble milkshake. But in 2019, they became such pervasive political weapons that when Nigel Farage went to campaign for his Brexit party in Scotland, police asked the local branch of McDonald’s to take them off sale. So loaded was their ideological significance that for publicly flouting and mocking that ban in a tweet, Burger King was sanctioned by the Advertising Standards Authority for inciting antisocial behaviour.

By the eve of European election polling day, just the sight of a milkshake was enough to paralyse the Brexit party campaign, with Farage forced to remain on his bus in Rochester, Kent, after three young men dressed in black and carrying milkshakes were spotted among crowds awaiting his arrival.

The Milkshake Spring began in May, when a 23-year-old customer services apprentice, Danyaal Mahmud, was captured on video in Warrington, Cheshire, tipping a milkshake over Tommy Robinson.

The imagery was potent: a handsome, slightly built Muslim youth face to face with Britain’s most notorious anti-Islam campaigner.

“At first I was like: wow, I’m actually standing in front of this guy,” says Mahmud, now a fully fledged customer services practitioner. “I was like: am I even breathing the same air as him?

“But then, after it sank in, when he started with his racist, abusive comments and threatening behaviour, the rest obviously was all on the news – and all over Facebook and Instagram and social media ... It was a massive thing.”

Robinson had been hit by a milkshake earlier that week, with a member of the public launching one at him from distance. But Mahmud was standing right in front of him and the impact was dramatic. Robinson lunged at him and threw punches until he was pulled away.

The impact of that fleeting moment on Mahmud’s life was enormous. “I had people coming over to me, taking selfies wherever I went,” says Mahmud. “I was getting thousands of messages, literally thousands. I’ve still not read through them all. Dessert bars was offering me to come over, saying: ‘Have a dessert on us and do promotions for us,’ and stuff like that. People were offering me limousines, car-hiring firms were saying: ‘Come hire a car from us for free.’”

The comedians Guz Khan and Tez Ilyas both searched Mahmud out, taking him out for meals and offering him parts in their television shows. He even had a private audience with Jeremy Corbyn when the Labour leader came to visit Blackburn.

Despite many people who regarded him a hero, there were those who hated him for what he did. He began receiving death threats. Police mounted extra patrols in his neighbourhood for security. Fearing for his safety and that of his family, Mahmud chose to stay quiet and let it all blow over.

He says his friends can’t understand why he didn’t want the attention. “Even now, to this day, my friends and that constantly pester me, like: ‘Why don’t you post anything online ever? Put something on Instagram. Why don’t you just post what you are eating or something like that?’”

“And I go: ‘I’m not that kind of person.’” He watched the milkshake saga play out online. “To be honest, after a while, it got a bit boring for me.”

The McDonald's next to the Farage demo. Someone clearly got wind. pic.twitter.com/kHETQ66TOq — Scott Macdonald 🏳️‍⚧️🏳️‍🌈 (@scott_eff) May 17, 2019

As Mahmud stayed under the radar, “milkshaking” entered Britain’s political language. Milkshake memes oozed over the websites and social media of leftwing activist sites. Calls went to “lactose the intolerant”. The right were said to be “milkshook” as other victims were targeted. Carl Benjamin, the YouTuber turned Ukip candidate who was investigated by police for saying he “might” rape the MP Jess Phillips, was hit in Totnes. Then, despite the presence of two bodyguards, Nigel Farage was soaked with a £5.25 banana and salted caramel shake from FiveGuys while out campaigning in Newcastle. As Farage’s assailant, Paul Crowther, was dragged away in handcuffs, he described his milkshaking as “a right of protest”.

A judge did not agree, instead labelling the 32-year-old’s deed an “act of crass stupidity” and – after convicting him of common assault – fining him £520, including £350 compensation to Farage. In a subsequent interview with Nick Ferrari on Global Radio, Crowther said he regretted his act, and told how the incident was “a moment of madness” that had led to him losing his job.

Disquiet over milkshaking went to the very top of British politics. Downing Street said of the phenomenon: “The Prime Minister has been clear that politicians should be able to go about their work and campaign without harassment, intimidation and abuse.”

Mahmud was not enthused as he watched the events unfold. “I mean, at the time, it was quite, it was quite violent,” he says of the run of incidents. His experience has not spurred him to get involved in campaigning. If he had the opportunity to live the milkshake incident over, would he do the same again? Not necessarily, he says.

“I did see a girl, ages ago, she wore a hijab and she stood at Tommy Robinson march. And she stood there and smiled, she never talked one bit. And after the milkshake incident, she really inspired me and motivated me thinking, hold on, that is more humiliating than throwing a milkshake over someone. Standing in front of them, you’re the only Muslim there. It’s more humiliating than throwing a milkshake.

“Just stand there, and just smile it off. And that’s it.”

• This article was amended on 13 December 2019 because an earlier version was incorrect to say that Paul Crowther was not willing to speak to the Guardian. Since publication he got in touch to say that the reporter’s messages had not been passed to him.