Two ministers, an MLA and a former mayor of Calcutta were brought to the CBI office here at Nizam Palace on Monday morning in connection with the five-year-old Narada scam, amid deteriorating relations between Bengal and the Centre.

The current mayor and the state transport and housing minister Firhad Hakim, panchayat minister Subrata Mukherjee, Kamarhati MLA Madan Mitra and former mayor Sovan Chatterjee were brought to Nizam Palace a little after 9am for questioning in connection with the televison sting in which several politicians and police officers were caught on camera allegedly accepting bribes from a fictitious company.

Chief minister Mamata Banerjee is understood to have reached the CBI office too on her own accord.

"I came to meet them," Mamata told newspersons upon reaching there, but sources close to her said she has vowed to stay put till such time the CBI released her party leaders.

Before leaving his Chetla residence, which was surrounded by personnel of the central forces, Hakim said he had been arrested.

“CBI arrested me in the Narada sting operation. I have been arrested without any prior notice,” he said before boarding a CBI vehicle. “I will challenge this in court.”

Sources said West Bengal governor Jagdeep Dhankhar had given the nod to prosecute the ministers. Charge sheets are scheduled to be filed against the four accused in the CBI court on Monday, they added, and that the four were brought in for questioning on Monday morning.

However, the CBI is yet to issue a statement .

Questions are been raised on procedure followed by the central investigative agency while detaining the the four for questioning.

First, no permission was taken from the Speaker’s office before proceeding to question/ detain the two ministers and an MLA.

“Clear indicators of mala fides of central government and CBI regarding West Bengal arrests. Necessity of arrest must exist before arresting. Power of arrest never means obligations to arrest. Narada is a decade old; even tapes are of 2016; matter also came to Supreme Court; why necessity to arrest now?” asked Abhishek Manu Singhvi, Congress Rajya Sabha MP from Bengal and senior lawyer.

“West Bengal arrestees cannot be proceeded against without Speaker’s sanction. Hence lack of jurisdiction plus vindictive arrest plus timing of arrests, all smack of, steeped in and clearly proves cheapest and most vile vendetta,” he tweeted.

After the Narada tapes were made public during the run up to the 2016 Assembly polls chief minister Mamata Banerjee had said she would not have given tickets to any of the accused if she had known. The accused went on to win the elections in 2016 _ and 2021 _ and are still ministers in her government.

Many of the names that came up in connection with the scam are now prominent faces of the BJP in Bengal and elsewhere.

The Calcutta High Court had ordered a CBI inquiry into the scam in March 2017. Charge sheets were filed against 13 leaders and other functionaries of the Trinamul Congress.

For these five years, the BJP was accused of using the Narada sting to further its own political interests in the state, where it fought a high-pitched campaign during the recently concluded Assembly polls but fell far short of the majority mark.

Chatterjee, the former mayor of Calcutta, had earlier quit the Trinamul and joined BJP. However, he wasn’t given a ticket in the Assembly elections and is not associated with the party any longer. Mitra, who won from the Kamarhati Assembly seat this time, was earlier arrested by CBI in connection with the Saradha scam.