Calcutta: The Opposition has started whetting its knives for an all-out attack on the Mamata Banerjee government on Thursday when the Lokayukta (Amendment) Bill will come up for discussion as it virtually leaves the chief minister outside the purview of scrutiny.

The bill will amend the West Bengal Lokayukta Act, 2003 - enacted by the Buddhadeb Bhattacharjee government - that had not provided for such exemption for the chief minister.

The earlier bill was passed in the Assembly in 2003 and notified the next year.

"This is outrageous and hilarious. Why is Mamata Banerjee, the 'embodiment of honesty', according to her acolytes, so afraid? Buddhababu wasn't," Left legislature party leader Sujan Chakraborty said on Tuesday shortly after the West Bengal Lokayukta (Amendment) Bill, 2018 was circulated among MLAs.

Chakraborty sat in the chamber of leader of the Opposition Abdul Mannan in the Assembly for several hours on Tuesday and the two carefully examined the bill.

The Opposition's ammunition is in one of the concluding paragraphs of the amendment bill, which prohibits "any investigation of any complaint relating to allegation of corruption against the Hon'ble Chief Minister relating to public order".

The bill, Opposition said, throws a similar immunity around any public servant as probes cannot be conducted now without the approval of the state government.

The amendment, according to sources, was an after-thought. #"It has been brought only after Bengal and 10 other states were directed by the Supreme Court in March to explain what steps they had taken to appoint the anti-corruption ombudsman, the Lokayukta," said a Trinamul MLA.

Mannan and Chakraborty pointed out two key aspects of the amendment.

First, the bar on the probe against the chief minister "relating to public order" virtually grants the occupant of the post complete immunity as all decisions of the chief minister can be described as acts related to public.

Second, the need for the government's approval for any investigation into a complaint against a public servant will make the ombudsman virtually toothless.

"She (Mamata) wants to be judge, jury and executioner, while taking herself out of consideration. A classic move of a totalitarian ruler," said Mannan.

The Lokayukta's recommendations, however, are not binding.

No senior Trinamul MLA wanted to comment on record. But some Trinamul leaders said on condition of anonymity that the bill was not inconsistent with Trinamul's stand in Parliament on the issue.

"Trinamul and AIADMK were the only two big parties, as early as 2011-12, to oppose before a Parliamentary standing committee the proposal for the compulsory inclusion of chief ministers in the ambit of the Lokayukta, calling it an attack on the federal structure," said a Trinamul source.

"The Prime Minister has been accorded virtually full exemption in the Lokpal provisions. Why should there be different rules for the chief ministers?" he asked.