Anti-Brexit MP Anna Soubry has said she was too frightened to speak at a rally outside Parliament, during angry protests in central London.
Police on horseback intervened as two groups of pro and anti-Brexit supporters gathered on Parliament Square in Westminster on Saturday.
About 200 people joined a pro-Brexit demonstration organised by the Democratic Football Lads Alliance (DFLA) while anti-Brexit group March for Change held their own protest.
As March for Change began to set up their rally, some members of the DFLA approached and began shouting.
A beer can was thrown towards about 10 people from the March for Change protest, before police intervened.
March for Change organisers said they had cancelled plans to float a Boris Johnson-shaped "blimp" due to the likelihood it would become a target.
Ms Soubry, leader of the Independent Group for Change, told organisers she was too frightened to speak due to intimidation from the counter-protests held by the DFLA.
Speaking to the PA news agency she said: "I don't know what I'm going to do.
"It's awful but there's also a side of me that thinks that this is our country.
"I'm a parliamentarian and I have a right to speak and I shouldn't be frightened but it's very, very, very disturbing, and I'm very frightened actually."
After consulting with the police and protest organisers, Ms Soubry left the rally, telling officers she did not want to cause additional issues for them as they monitored both events.
Tom Brufatto, a director of the March for Change, said protesters were there to "demonstrate peacefully and defend our democracy".
He added: "We have been attacked three times. We respect people's right to protest but we do not respect people's rights to intimidate and be aggressive."
Hundreds of people also gathered outside nearby Downing Street on Saturday, to demand Boris Johnson's resignation.
Organised by groups including Another Europe is Possible, Momentum and the Green Party, the Demand Democracy: Johnson Out protesters said the Prime Minister was "attacking democracy".
Speakers at the event included Labour MP Diane Abbott and Green Party co-leader Sian Berry, while protesters carried signs bearing messages such as Stop the Coup and Migrants welcome.
A human barricade of police was formed after a small group of pro-Brexit protesters started attacking police officers.
The march was eventually allowed to start, surrounded by a heavy police presence, occasionally pausing in a tense stand-off with counter-protesters.
Marchers chanted "fascist scum off our streets" and "refugees welcome".
Ms Berry also addressed the rally in Parliament Square and praised the work of opposition MPs for proposing and passing a Bill to prevent a no-deal Brexit prior to the suspension of Parliament.
Addressing the pro-Brexit protesters on the other side of the square, she said: "That's why they're here today, they know they're losing."
During speeches, the crowd of several hundred people started cheers of "bollocks to Brexit" and "bollocks to Boris".
Rows of police, including officers on horseback, stood between the two groups of pro and anti-Brexit protesters.
Some members of the protest organised by the DFLA were seen throwing eggs at people filming them.
Labour and Co-operative MP Lloyd Russell-Moyle called Brexit "evil" in a passionate speech delivered at the rally.
He said: "Every day that passes that we remain in the European Union is a victory to our movement.
"While some call us traitors, we are not the ones trying to break up this country and turn it into an English, white nationalist country, they are.
"We are not the ones destroying the rights of migrants, they are. Just like all things, good will triumph over evil and Brexit is evil."
The MP also accused Leave-supporting politicians, including Jacob Rees-Mogg, of aspiring to turn the UK into a "nasty feudalistic country".
Speaking about the possibility Parliament will be suspended next week, he added: "We MPs will continue to sit in Parliament and we ask you to set up a community People's Parliament across the country."