About 4,000 people joined former English Defence League leader Tommy Robinson in a protest against the BBC.
The corporation confirmed an upcoming Panorama episode was investigating Mr Robinson, whose real name is Stephen Yaxley-Lennon.
He criticised the programme at the rally outside the BBC’s Salford offices. About 500 people attended a counter-protest by anti-fascists.
The BBC said the episode would follow its “strict editorial guidelines”.
Mr Yaxley-Lennon said the aim of the protest was to make a stand “against the corrupt media” and called for the BBC licence fee to be scrapped.
During the rally, undercover filming of BBC Panorama journalist John Sweeney, carried out by a supporter of Mr Yaxley-Lennon, was broadcast on a large screen.
Mr Sweeney is heard saying “one of my political heroes is the former head of the IRA Martin McGuinness”, which the BBC says was taken out of context as Mr Sweeney was referencing Mr McGuinness’s role in the peace process.
Mr McGuinness, who, as a prominent Sinn Fein politician, became Northern Ireland’s deputy first minister, had acknowledged he was a member of the IRA. He died in 2017.
Mr Sweeney was also recorded making remarks which Tommy Robinson has described as racist, homophobic and anti-working class.
In response, a BBC spokeswoman said: “The BBC strongly rejects any suggestion that our journalism is ‘faked’ or biased.
“Any programme we broadcast will adhere to the BBC’s strict editorial guidelines.
“Some of the footage which has been released was recorded without our knowledge during this investigation and John Sweeney made some offensive and inappropriate remarks, for which he apologises. BBC Panorama’s investigation will continue.”
UKIP leader Gerard Batten told demonstrators that Mr Yaxley-Lennon “speaks up for things that are right, he tells the truth and he can mobilise lots of people like you, and that’s what they fear”.
A rally organiser also took to the stage and told demonstrators: “Don’t touch the photographers or any of the media companies. Let them be. Just for today.”
The National Union of Journalists (NUJ) said they “roundly condemn Tommy Robinson… and his fellow, far-right thugs who intend to intimidate staff at the corporation, particularly those working on Panorama”.
“BBC staff should be free to do their jobs without these threats,” the NUJ spokesperson added.
“Intimidation, threats and violence carried out by far-right protesters systematically targeting the media, especially photojournalists, are becoming more frequent and we will always call out this behaviour and report criminal activity to the police.”
In May 2018, Mr Yaxley-Lennon was jailed for potentially prejudicing two court cases – in Canterbury and Leeds – after having been found to have broken contempt of court laws by live-streaming outside them on social media.
The Court of Appeal later quashed the Leeds conviction and ordered that it be reheard in its entirety.
Mr Yaxley-Lennon is waiting for a decision from the attorney general on whether he will face a full trial for the alleged contempt outside Leeds Crown Court – the ruling that he committed contempt of court by live-streaming in Canterbury still stands.
He told the Salford protest: “I want us all to give him a message… I dare you to charge me again because I just want to see the scenes outside court.”
In November, PayPal announced it would no longer process payments for Mr Yaxley-Lennon, saying he had broken its policy on acceptable use.
He was banned from Twitter in March 2018. It is understood that his account was suspended for breaking its “hateful conduct policy”.
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