The civic authorities have been jolted by the discovery that a section of builders in the city has illegally constructed scores of low-end multi-storeyed buildings, comprising thousands of flats, without underground (septic) tanks.

Mayor Subrata Mukherjee said on Wednesday that areas like Kidderpore, Tiljala, Topsia and parts of Ballygunge, Bhowanipore and Tollygunge are witnessing regular choking of the drainage system because of direct flow of waste matter from these apartments to the drains.

According to a civic drainage department estimate, over 2,000 such flats have come up in the slum areas of the city over the last six years.

?Mushrooming of flats without proper toilet facilities is threatening the city?s overall environment. A section of third-class promoters, patronised by leaders of the ruling parties, are responsible for this,? said the mayor.

According to him, vote-bank politics is hampering the development of the city and political leaders should rethink whether they will continue to support people who are indulging in such illegal activities.

Calling these promoters and their political bosses ?enemies of society?, the mayor said: ?They construct illegally and disappear after pocketing the profits. The civic body has to face the consequences.?

?If this nuisance is not stopped right now, the Asian Development Bank-sponsored Rs 1,245-crore Calcutta Environment Improvement Project will turn out to be a big flop,? warned Mukherjee. He said the political leadership was allowing the promoters to add to the pollution load on the city?s environment.

Mayor-in-council member (drainage & sewerage) Mala Roy said the problem is so acute in some slums in Tiljala, Topsia, Rajabazar, Ekbalpore, Chetla, Kidderpore, Tangra, Pearabagan and Darapara that the drains overflow even when it is not raining.

Mayor-in-council member (slum development) Javed Ahmed Khan held the state government responsible for the menace. He alleged that despite repeated requests, the government did not allow the Calcutta Municipal Corporation to construct buildings for rehabilitation of slum dwellers.

The plots on which the buildings have come up belong to the controller of Thika Tenancy. ?It is strange that the controller of thika land is not taking steps against the promoters,? Khan added.