Transport Secretary Sumantra Chowdhury had lodged a complaint with the Hare Street police station on December 4 and requested the Detective Department to start a probe into reports of transport permits being issued on the basis of fake challans.

According to a senior transport official, the scam was noticed after a computer in the department detected two challans with the same serial number, which appeared to be issued by the Reserve Bank of India (RBI). State Transport Minister Ranjit Kundu then initiated a departmental inquiry.

The police today arrested Bablu Dey alias Prabir Dey (43), a resident of Belgharia, Mahadeb Brahma (38) of Sodpur and Bapi Kodali alias Khagendranath Kodali of Shibpur.

The permit, for which the challan was duplicated by Bablu Dey, was issued in the name of Sadbir Singh, a truck owner of North 24-Parganas.

“We have arrested three persons and they have been sent to police custody for 14 days. It seems there is a bigger racket operating in the challan forgery business. Several other people are also involved. An investigation is on,” said Damayanti Sen, Deputy Commissioner, DD.

According to a transport department official, the loss to the state exchequer has been estimated in crores. The police are yet to ascertain the exact amount of loss.

“A large number of touts operate in the transport department who get permits done for the vehicle owners. After the scam was revealed, we have received an order from the minister not to allow touts inside the department,” said the official.

“We have asked the transport department for a few documents, which we are yet to receive. Meanwhile, they have started a departmental inquiry,” said Sen.

A senior police officer said the possibility of transport department officials being involved in the scam cannot be ruled out.