The CBI’s “misadventure” in Calcutta had the stamp of approval from one of the most powerful politicians in the country, a senior government source familiar with the functioning of the agency told The Telegraph on Monday.

“The tension was brewing for the past few weeks between the BJP and the Bengal government for obvious reasons, including the Mahagathbandhan rally in January. The CBI’s unprecedented siege of the official residence of the Calcutta police commissioner has approval from this leader who has no direct role in the government,” said the source who did not want to be named as he is not authorised to speak to the media.

The government official was by no means trying to defend the city police. On the contrary, the official made the disclosure about the purported political driving force behind the operation while insisting that the Calcutta police commissioner was a “suspect” in the case and he was not co-operating with the probe.

“The Saradha scam is a politically sensitive case. The final decision to go ahead with the operation at the commissioner’s residence in the evening was taken after consultation with this political leader,” the official added.

The government official drew a parallel between the midnight surgical strike at the CBI headquarters in October and the Sunday siege in Calcutta, suggesting a political common factor in both actions.

Asked about the curious timing of the crackdown — the day turned out to be the last of Nageswara Rao as interim director — another official said: “It was decided to conduct the raid and question Kumar on Rao’s last working day so that the new director does not have to face allegations of acting on the instructions of the political masters.”

“Who knows, the new director could have put his foot down?” the official added.

The new director, Rishi Kumar Shukla, took charge on Monday. Shukla refused comment on the Calcutta showdown.

Rao was appointed interim chief hours after the midnight raid in October, which led to the benching of the then CBI director Alok Verma.

Sources said senior CBI officers were holding meetings with the central government’s lawyers and were busy collating evidence to be presented before the apex court on Tuesday morning.

“The CBI joint director posted in Calcutta has reached Delhi to help make a watertight case,” said an officer.