The Audi Q7 that breached a high-security corridor and ran over an air force corporal on Wednesday morning had broken the first rule of the road the day it rolled out of the showroom without a registration number.

The family of Trinamul leader Mohammad Sohrab isn't the only one to have gotten away with using a new vehicle before the completion of the registration process. Cars with TC (trade certificate) plates are a common sight in Calcutta, an illegal practice that has gained currency because of police's reluctance to slam the brakes.

A TC number is little more than a temporary authorisation of transit in specific conditions. By the book, the owner of a new car is not supposed to take possession of the vehicle until the registration is complete.

The public vehicles department, of course, has never bothered to find out how many vehicles ply with TC plates. Post-Wednesday, the department has written to the Audi dealership on AJC Bose Road asking why it shouldn't be penalised for handing over a new Q7 to its owner without the registration coming through.

Mohammad's eldest son Ambia Sohrab, 26, had purchased the car nine days before the incident. The vehicle's ownership is in the name of a company called Mussadi Business Pvt. Ltd, of which Ambia and his younger brother Sambia are directors.

"The dealership has been given a week to respond. If it doesn't, we might cancel its licence," a PVD official said.

Metro highlights why it is illegal to drive around with just a TC number and how the car dealership is culpable for any such violation.

What do the rules say?

Section 44 of the Central Motor Vehicles Rules, 1989, states: "If the registering authority has reason to believe that the holder of any trade certificate has not complied with the provisions, it may suspend or cancel the trade certificate held by him after hearing him out."

What are these provisions?

Section 41 states that a trade certificate holder "shall not use any vehicle in (a) public place...". The specific instances when the vehicle can be used with a TC number are: for a test, by or on behalf of the holder of the trade certificate during repair; to proceed to or return from a weigh bridge; for a trial for the benefit of a prospective purchaser; to proceed to or from the premises of the dealer or purchaser; to proceed to or return from a workshop or an automobile expo and, lastly, to remove the vehicle after it has been taken possession of by a financier.