Law Minister Ashwani Kumar quit on Friday after becoming the face of the government’s interference in the CBI’s “coalgate” probe.

An angry Supreme Court judge berated the CBI on Thursday in his statement on the elite agency’s involvement in the scandal.

Justice RM Lodha called the agency a "caged parrot" and "its master's voice" after it was revealed that the CBI presented a draft report of its investigation into the coalgate scandal to government officials before submitting it to the Supreme Court last year.

The Supreme Court was provided with a nine-page affidavit from CBI director Ranjit Sinha detailing who the draft was presented to and what changes were made.

The Indian Express reported that in his affidavit Sinha cited two "significant" changes made in the report after Kumar's intervention but neither of the changes made had "altered the central theme of the report, nor shifted the focus of inquiries or investigations in any manner”

But Lodha disagreed, stating in court that the "heart of the report" had been altered, a damning statement for the CBI which proudly proclaims its motto to be "industry, impartiality and integrity".

Kumar’s resignation has added to speculation the prime minister may have to call an early election amid government in-fighting.

The Times of India reported Tuesday that following the Supreme Court scorching the government had formed a group of ministers to draft a law to protect the CBI from external influence.

It will be headed by the finance minister and receive input from Sinha.

“The group of ministers will deliberate on ways to further strengthen CBI's autonomy and safeguard it from any kind of outside interferences,” official sources told the newspaper.

It was also reported that the comptroller and auditor general has started a second audit of allocated coal blocks to ensure tariffs have been adequately set.