For the same reason, all over North 24-Parganas autos are using diesel -- again illegally-- that costs Rs 1.80 per km. These vehicles, bigger in size than petrol autos, can now be found even in Behala, Tollygunge and Metiabruz.

"It is not possible to register diesel autos anywhere in the entire Calcutta metropolitan area because they do not meet the specified pollution norms but it's a fact that many are illegally plying in the area," Banerjee said.

He added that such diesel-run autos are often caught and penalised.

Asish Chowdhury, who owns a diesel auto, said the administration had not heeded their appeal to allow the vehicles to be registered.

"Nearly 15,000 diesel autorickshaws, all unregistered, are running in North 24 Parganas," he said.

Local sources said each diesel auto owner paid a minimum of Rs 30 daily to the union in return for the protection they received. In Barasat alone, over 100 such autos would deliver around Rs 1 lakh a month to the union.

For autorickshaws, in Calcutta and elsewhere, all roads lead to the union.

It will be wrong to think that though domestic LPG is being used illegally, there will at least be a green dividend. Experts say the use of domestic gas as transport fuel is polluting because the composition is vastly different. Being used for a purpose not meant to, it's also fraught with risks of accident.