When Nigel Farage used a radio interview this week to publicly attack Brendan Cox, husband of the murdered Labour MP Jo Cox, he lashed out in the most unbelievable way. Just six months after Jo was murdered by neo-Nazi Thomas Mair, the former Ukip leader attempted to pin the extremist tag on Brendan Cox because of his association with the organisation I head, Hope not Hate.

Even by his standards, Farage’s comments were disgustingly offensive. Many were outraged, not just us.

After we demanded an apology from Farage, his most loyal supporters leapt in. Arron Banks, the millionaire businessman who bankrolled Ukip and the Leave.EU campaign, took to Twitter to call us a “vile organisation”. He outrageously claimed we had “organised a mass confrontation” against Farage.

Raheem Kassam, the British editor of the US far-right website Breitbart, and Farage’s former chief strategist, began crowdfunding to finance research on us. We have also received thousands of abusive and threatening tweets, Facebook posts, emails and phone calls.

This is how these people operate. They attempt to vilify, abuse and bully their opponents into silence. Whether it is Farage in the UK or Donald Trump in the US, they think they can demonise their opponents without any thought for the damage it causes or the anger and hatred it incites in their supporters. And it’s a David v Goliath struggle, where the other side portrays itself as the underdog yet in reality is backed by an online army and millionaires in the wings.

Facebook Twitter Pinterest ‘Whether it is Farage in the UK or Donald Trump in the US, they think they can demonise their opponents without any thought for the damage it causes.’ Photograph: Murdo Macleod/The Guardian

Farage dislikes us because we have shone the spotlight on Ukip and played a part in stopping him getting elected in Thanet. He and other Ukip elected officials and party members responded by calling us names and abusing us.

We began targeting Ukip in 2013 as it started adopting a more anti-immigrant stance, specifically whipping up scare stories with claims that 29 million Bulgarians and Romanians would come to the UK. Events since have proved we were right to do so.

When we tried to meet the party leaders to discuss the issue of its growing extremism, they failed to turn up to their own meeting. Not only that, the party’s conference then passed a motion banning any Ukip member from supporting Hope not Hate.

Over the next few years we exposed their racist and homophobic councillors, the strongly anti-Muslim views of some of its MEPs, as well as links to European far-right parties, and highlighted the lies and exaggerations in its election leaflets.

Of course Farage and supporters such as Kassam conveniently ignore the community campaigning we carry out across the UK. We rely on a network of thousands of volunteers up and down the country, bringing together tens of thousands of people to celebrate a shared sense of community across apparent cultural and religious divides.

Facebook Twitter Pinterest ‘Raheem Kassam, the British editor of the US far-right website Breitbart, and Farage’s former chief strategist, began crowdfunding to finance research on Hope not Hate.’ Photograph: Neil Hall/Reuters

From family fun days, picnics, food festivals and encounters between those of different faiths and none, we have enabled people to celebrate all that they have in common. Part of this work was our national #MoreInCommon campaign, launched in response to the murder of Jo Cox (with the support of her family) and to counter some of the negativity surrounding the EU referendum campaigning. We hosted 85 events across the UK, bringing communities together.

Earlier this year we stood fast with Birmingham’s Muslim community, creating a unity pledge with all the city’s main leaders, in response to a threatened far-right demo by Pegida UK.

Last summer we did the same with the Jewish and other community members in Golders Green, north London, dressing the entire area in gold and green ribbons, before a neo-Nazi march. In Merthyr Tydfil we organised a football match between the local team and Portuguese and Polish migrants as a bridge-building exercise.

As we have seen so graphically this year, the lies of the populist right have consequences. They toxify debate, bully people into silence and whip up an angry base. That’s why it’s time to draw a line in the sand, and why we have demanded a retraction and an apology from Nigel Farage. He cannot keep getting away unchallenged with his lies any longer.

But this issue is far bigger than just the words Farage used against us. It is about the politics of hope and hate. As Edmund Burke wrote: “The only thing necessary for the triumph of evil is for good men to do nothing.” So if you are horrified by the rise of the far right, whether that be rightwing populists or more traditional fascists, then we urge everyone to do what they can to support those, like ourselves, who want to protect communities from further division and hatred.