LONDON (Reuters) - Anti-racism activists say they acted quickly to get people to come together to stop days of far-right rioting in Britain but that the main test for their fight against hate lies ahead.

Jo Cardwell, 51, is a volunteer at Stand Up to Racism, which was behind many of the counter-protests challenging the racist violence that has shaken communities in recent days.

After more than three decades of activism, she knew the movements had to activate national anti-racism networks fast when far-right groups opposed to immigration and others began targeting Muslims, Black people and asylum seekers last week.

"In many places, we were ready but we need more people all the time," said Cardwell, who was chief steward at Wednesday's biggest anti-racism protest in Walthamstow, north London. "This is a scale of attack that we have never seen before."

In scenes echoed across the country, crowds holding banners and chanting 'Refugees are welcome here' gathered outside an immigration advice centre in Walthamstow that had appeared on a list of far-right targets posted online, fending off potential threats. Officials said strong policing also put off the rioters.

"Our society is richer because of multiculturalism, it is richer because of the people who have come here," Cardwell said ahead of the protest. "These are things that should be celebrated and fought for, not things to be feared."

The riots began after a wave of false online posts wrongly identified the suspected killer of three young girls in a knife attack on July 29 in Southport, northwest England, as an Islamist migrant.

An estimated 25,000 people joined counter-protests across Britain on Wednesday alone, largely outnumbering the far-right, thanks partly to well-established contacts with trade unions, religious groups and the labour movement, Cardwell said.

Peter Achan, an activist who also attended the Walthamstow protest, said it was crucial for communities to continue to come together to "stop the hate".

"If we don't stand up against it, there is more chance this hate will continue to grow," Achan said.

Both the far-right and those opposing them have been using social media to share information about gatherings and events.

Telegram is known to be the far-right's go-to platform, but counter-protesters are also active on it, with one of their main groups having more than 3,000 subscribers. Other platforms, such as WhatsApp and Tiktok, are also key.

"Social media has changed some of their (far-right) organising models so we have to be on top of that: where are they organising, who are their organisers and what are they planning," said Asad Rehman, chair of anti-racism organisation Newham Monitoring Project.

With immigration lawyers and mosques reportedly on far-right hit-lists and some people targeted just for looking or sounding different, the 57-year-old said the work of anti-racism groups includes ensuring they are equipped to send immediate support to the scenes of racist incidents or places under attack.

'TIDE OF HATRED'

In Walthamstow and at other counter-protesters across the country, many pro-Palestinian activists turned up with flags and signs saying "Make love not war".

Among the disparate groups attending the counterprotests were some wearing facemasks while others were filmed carrying bats and other such weapons, prompting organisers to urge attendees to behave.

At demonstrations in the past, there have been violent clashes between far-right groups and counter-protesters, with both sides blaming the other for starting the trouble.

Cardwell said migration policies introduced by the former Conservative government, including a much-criticised scheme to send asylum seekers to Rwanda, had made people more aware of the need to fight far-right narratives. The Conservatives have condemned both far-right narratives and the latest violence.

Both Cardwell and Rehman said it was important to tackle the "roots" of the upsurge in far-right violence which they argue lie in years of wrongly blaming migrants and other ethnic groups for falling living standards, by some media and politicians.

"Politicians are telling us to worry about the people (arriving in the UK) in small boats," Cardwell said. "(But) it is the people in private jets and superyachts I'm worried about."

Further counter-protests and far-right riots are expected in upcoming days, with authorities remaining on alert.

(Reporting by Catarina and Marissa Davison; Editing by Philippa Fletcher)

By Catarina Demony and Marissa Davison