The decision to appoint former justice Shivaraj Patil to look into the procedures of the telecom ministry in awarding mobile licenses and spectrum between 2001 and 2009 comes as part of a wider probe into the multi-billion-dollar scandal.

“We are trying to find out through a transparent, independent process what happened,” Telecom Minister Kapil Sibal told reporters in New Delhi.

Sibal's predecessor, A. Raja, was forced to quit last month over accusations he sold mobile licenses in 2008 at knock-down prices, costing the treasury up to $40 billion in lost revenue, according to the national auditor.

Patil “would seek to identify any lack of transparency, deficiency in procedures, lapses, if any, at the policy and procedural level and whether there were any policy violations”, Sibal said.

“We are relying on a retired Supreme Court judge to tell us what was right and what was wrong,” he said.

India on Thursday widened the probe into the country's biggest corruption case to include decisions made during the main opposition party's rule, a move that may take steam out of a campaign against the government.

The probe into the 2008 grants of telecoms licenses that the state auditor said lost India $40 billion in potential revenue will now examine licensing procedures when the main opposition was in power and which have been cited in court as a precedent.

The opposition Bharatiya Janata Party (BJP) has forced Parliament shut, demanding the Congress-led government set up a parliamentary probe into the case, the largest of a raft of corruption cases that have emerged in recent months.

Sibal's decision to ask a retired judge to probe decisions from 2001 onward, which would include those of the BJP during its rule until 2004, could put the party on the defensive and allay fears the political deadlock could spill over to the February session of Parliament.

Raja had defended himself saying he followed past norms and the Supreme Court had asked police working on the case to look back to 2001.

Singh and his government have been struggling to contain the damage from India's “season for scams” which includes a bribe-for-loans scandal which implicated state-run banks and sizeable private companies and, graft at the Commonwealth Games. The cases have taken the sheen off India's image as an investment destination, and the parliamentary deadlock has delayed the passage of key reforms including a much awaited law for the easing of land acquisition for industry.

Investors have shrugged off widespread corruption as part of the risk of doing business in emerging markets, but remain wary of any regulatory changes and of decisions that could affect existing foreign investments, such as those made in telecoms firms being probed.

On Thursday, top Indian mogul Ratan Tata appeared to give some support to the government, citing telecoms policy “flip-flops” during the BJP's rule and terming the auditor's estimate of losses as “hypothetical.”

“Whatever may be said, it must be recognized that the recent policy broke the powerful cartel which had been holding back competition and delaying implementation of policies not to their liking,” Tata said in a letter released by his publicist.

Ratan Tata, ranked No. 61 in the Forbes list of the world's most powerful people, and his $70 billion conglomerate are seen as refreshing exceptions in a country where corruption is widespread and often accepted.

Sibal said India will issue notices later this week to several companies, asking them why their telecoms licenses should not be cancelled, after the audit report suggested they were not eligible for them.

The companies named in the state auditor's report on the scam include those which were later bought into by Norway's Telenor and UAE's Etisalat . The ministry is also sending separate notices to 119 zonal telecoms licensees that have not complied with services roll out obligations.