The case was registered at Hastings police station on a complaint lodged by sub-inspector Apu Baidya, a senior Kolkata Police officer said. "He alleged that Mamata and organisers of the Trinamool Chhatra Parishad rally criminally conspired to violate the high court's order," the officer said.

The complaint alleges that Mamata provoked supporters during the rally, held between noon and 3pm.

The crowd allegedly pushed aside barricades, "jostled with police personnel deployed to maintain law and order, created a chaotic situation and obstructed vehicular movement on one flank of Cathedral Road", the complaint stated. It also alleged that the programme continued beyond the time permitted by the court.

Police said the FIR was registered under several sections of the BNS, including criminal conspiracy, rash and negligent acts endangering human life or property, disobedience of a public servant's lawful order, causing danger or obstruction on a public way, and deterring a public servant from discharging lawful duty. Most of the sections are bailable, while the last is non-bailable, senior officers said.

Mamata and Abhishek Banerjee were the key speakers at the rally, which the police said drew a crowd well above the permitted limit of 1,500.

The high court, while allowing the Trinamool and its rebel faction to hold separate Chhatra Parishad foundation day rallies on Cathedral Road and Rani Rashmoni Avenue, had directed organisers and volunteers to ensure that one flank of both roads remained open to traffic during the programmes.

Officers said preliminary examination of video footage showed traffic moving on one flank of Cathedral Road when the rally began. Later, the crowd standing behind guardrails opposite the main stage broke through the cordon and moved towards the dais where Mamata and other Trinamool leaders were standing, bringing traffic to a halt, they said.

The FIR was registered hours after chief minister Suvendu Adhikari directed the police to take action for the alleged violation.

"Did you see how the former chief minister violated high court orders? The order was to keep a flank of the road open. She called her supporters from beneath the shade of trees and blocked the flank," Suvendu said on Friday. "I have instructed the police to register an FIR against her and move court."

Trinamool leaders, however, said Mamata had herself asked supporters to clear the road when the crowd gathered near the dais. They said a line of vehicles caught in the snarl, as well as an ambulance, was allowed to pass. Mamata was heard asking party workers to listen to the police and make way for vehicles.

"The police couldn't control the crowd that gathered on Cathedral Road, and as a result, the barricades gave way. This was not Mamata Banerjee's fault," Trinamool MP Saugata Roy said. "The manner in which Suvendu Adhikari is trying to regulate crowd count for a political rally is against the rules of democracy. He is worried about the turnout at the rally," Roy added.

The state BJP leadership said that the police action was in line with the government's stated policy of establishing the rule of law.

"Trinamool has never cared two hoots about Calcutta High Court. But now, there is no place for any indiscipline," said state urban development and municipal affairs minister Agnimitra Paul. "The government won't function according to the wishes of Mamata and Abhishek Banerjee."