About 30 anarchists clad in black and with their faces covered staged the protest outside Shoreditch House, in east London.
Witnesses report seeing smoke bombs hurled towards the entrance to the building, where the Creative France UK launch event was being held.
French Ambassador for International Investment Muriel Penicaud was reportedly attending an event inside the building at the time the demonstrators gathered.
The activists – clutching banners bearing slogans in support of refugees – were angry at the clearance of the notorious Jungle migrant camp in Calais, France.
Police blockaded the entrance and advised passers-by to stay back as the protesters handed out leaflets criticising the French government”s decision to clear the camp.
A 27-year-old, from Haggerston, told the Evening Standard: “I was just walking back from work and there was a bunch of people who had their faces covered, it looked like they were trying to get into Shoreditch House.
“Police were blocking the entrance and members and non-members couldn”t get in the door.”
The protesters were handing out flyers and holding banners with anarchis symbols and slogans such as “Solidarity to Calais” and “No Borders”.
A Metropolitan Police spokesman said: “Police were called to Ebor Street, E1, to reports of a protest taking place at approximately 6.50pm.
“Officers are currently on scene. An appropriate policing plan is in place.”
Workmen began clearing the sprawling Jungle camp last month.
French authorities had given migrants living in the southern part until 8pm local time – 7pm GMT – on Tuesday to quit their makeshift homes or face bulldozers being sent in.
The Help Refugees charity said 3,455 people were living in the affected area.
But at the last minute a French administrative court adjourned a decision on the demolition in response to an appeal by activists and residents.
After hearing arguments on both sides, Judge Valerie Quemener said: “The decision will not be taken today.”