The action triggered a confrontation with Trinamool general secretary Abhishek Banerjee and party leaders and workers preparing for the Trinamool Chhatra Parishad's foundation day programme on Friday.

Police said 12 people were detained during the operation.

Abhishek accused the BJP of trying to forcibly weaken the party and said they would move the high court on Friday against the action.

"There is a planned attempt to finish the Trinamool Congress forcibly. Why is the BJP so scared? The ruling party and the administration are attacking leaders and breaking billboards," Abhishek said. "The Trinamool Congress symbol is a grass flower. The more you cut grass, the more it grows."

The building houses an I Love Haldiram store on the ground floor and Abhishek's office on the first. Senior Trinamool leaders said political strategy and consulting firm I-PAC had operated from part of the office during an election campaign. Corporate offices occupy the remaining floors.

Around 4.30pm, KMC officials arrived with an order to dismantle the billboard. Accompanied by officers from Shakespeare Sarani police station, they were confronted by Trinamool workers as they tried to reach the rooftop with gas cutters.

Abhishek demanded copies of the authorisation and the complaint that had prompted the action, leading to a nearly half-hour verbal standoff as he pointed out what he alleged were errors in the documents.

"The order states that there is a photograph attached 'for your perusal'. Where is that photograph?" he asked. "If there is a formal complaint, why were we not given a formal hearing before it was decided that the billboard would be pulled down?" he asked.

The KMC team returned to amend the paperwork and came back around 5.40pm with a reinforced police team, including women personnel.

A scuffle broke out as the officials and police tried to enter the building and reach the rooftop. Trinamool Rajya Sabha MP Derek O'Brien fell on the stairs amid the pushing and shoving. Women supporters shouted "Joy Bangla" slogans, while police alleged that their personnel were attacked.

O'Brien later posted on X accusing the police of illegally entering the building on the basis of an "unsigned, incomplete, error-filled KMC notice" and alleging "mayhem" and "police atrocities" against Abhishek, party men and MPs.

The teams eventually reached the rooftop after breaking open a door to access the structure supporting the billboard. Civic workers brought down the banner bearing the "All India Trinamool Congress" name and symbol before using a gas cutter to dismantle the iron scaffolding. The team left the building after 7pm.

Police subsequently picked up several people for allegedly attacking government officials and obstructing them from discharging their duties.

Abhishek, whose Kalighat house was raided by a Salboni police team on June 13 in search of his assistant Sumit Roy, criticised Thursday's action.

"West Bengal is witnessing the steady erosion of constitutional governance and an alarming descent into a police state," he wrote on X, adding that the judiciary was the "last line of defence" when fundamental rights were undermined.