Protesters succeeded in sabotaging a hustings organised for the Lewisham East by-election.
Police were forced to shut down the hustings in Catford, as tensions grew outside and anti-racism protesters clashed with members of the public.
One man was arrested on suspicion of assault, but released without charge.
Liberal Democrat and Women’s Equality party candidates have criticised the protest, saying it prevented opportunities to openly criticise far-right opinions.
While the Stand Up to Racism group, who led the demonstration, say it was justified because it stopped For Britain candidate Anne Marie Waters, who they believe is a racist, from speaking.
Doreen Cooper, 83, had walked to the Salvation Army building in Catford, where she regularly prays, to ask the question she had prepared for the candidates. But she was prevented from getting in.
Ms Cooper, who lives in Stannard Court, said: “It’s frightening. I don’t want to meet any of these people at night. It’s awful, people that can be roused with such temper.
“I was hoping to be able to get in to talk to the candidates, but it doesn’t look as if I’m going to get a chance.”
About 100 protesters arrived last night before the hustings was due to begin at 7pm.
They blocked the main entrance, trying to prevent candidates from entering.
A small police presence then opened up a side gate, letting a number of candidates into the building.
The protesters rushed over to block the side entrance.
Angry exchanges between the protesters and members of the public supporting the candidates ensued.
A larger police force was then called in with up to 30 officers attending.
The target of the protest, Ms Waters, did not turn up to the hustings.
She said on twitter: I can categorically state that I did not cancel my attendance at the Lewisham East hustings. We have been told to stay away by the police who have told my security team they are shutting it down.”
Ms Waters stood for UKIP in the general election in Lewisham East in 2015, coming third with 9.1 per cent of the vote.
She had previously been a member of the Labour party.
She also helped set up the UK branch of the anti-Islam group Pegida with Tommy Robinson and spoke at the “Free Tommy Robinson” march on Saturday in central London.
Lib Dem Lewisham East candidate Lucy Salek said: “Debate is at the very heart of democracy, and last night the people of Lewisham were been badly let down.
“I attended the hustings to stand up for the liberal values that the people of Lewisham hold dear. As a result of the actions of a few, my voice was stifled.
“In these strained times it is crucial that we allow those with opposing views to debate. Liberal values will win, every time.
“I will always defend the right to peaceful protest, but the toxic and threatening atmosphere outside the hustings last night was totally inappropriate.”
Mandu Reid, Women’s Equality Party candidate for Lewisham East, said: “I wanted to go to the hustings to challenge the far-right’s hate-filled narrative and to expose their ugly ideology for what it is.
“Unfortunately, I was denied that opportunity and, more importantly, the residents of Lewisham East were denied the chance to question their future MP.
“We cannot have a situation where parties on the hate-filled extremes of politics have a disproportionate ability to influence how our democracy works and it is frustrating that these far-right figures will now tediously and noisily claim that they are being silenced, with no counter-narrative on offer.
“Tonight, there was a vacuum where the biggest parties should have been standing shoulder-to-shoulder against hate. In recent years both have chosen an approach of absorbing what political benefits they can from these fringes and ignoring the rest – both polluting the mainstream and making the fringes more toxic in the process.
“Doing politics differently means showing up, even when it’s difficult.”
A spokesman for Stand Up to Racism said: ”
“The attendance last night of former members of the BNP, including their former elections chief Eddy Butler, representing Waters’ For Britain party, confirmed that our concerns for the safety of our diverse community were well founded.
“Lucy Salek and Mandu Reid are mistaken to think that we can win a civilized debate with Waters whose leaflets have included the line ‘all politicians lie’ and the racist dogwhistle ‘one law for all’ at the same time as she is campaigning for fascist former EDL leader Tommy Robinson to be exempted from the law after his jailing for contempt of court.
“Their claims that anti-racist protesters stopped the people of Lewisham having their say ignores the fact that the largest group of Lewisham residents attending were those joining the anti-racist protest and raising their voices in solidarity with our muslim neighbours targeted by For Britain.
“We commend all who turned out to make it clear the divisive, racist politics of Waters and For Britain are not welcome in Lewisham and all those candidates who listened to our concerns and put the safety of our diverse community first.”
A Met police spokesman said: “A pre-planned hustings event at the Salvation Army centre in Brownhill Road, on the evening of Tuesday, June, 12 was closed down with the permission of the event organiser, following concerns for public safety after a large crowd gathered outside the premises.
“The crowds dispersed; there were no reports of any injuries.”
The Lewisham East by-election was triggered by Heidi Alexander’s resignation last month, to join London Mayor Sadiq Khan at City Hall as deputy mayor of Transport.
Voters will go to the polls on June 14.