NEW DELHI: The Bharatiya Janata Party (BJP) on Friday said the "culpability" of P Chidambaram was evident in the 2G spectrum scam and demanded a fair investigation into his role as the finance minister in allocation of scarce spectrum in 2008.

Keeping up its attack on Chidambaram, BJP spokesperson Ravi Shankar Prasad said the government's image will be further tarnished if it does not order an investigation into his role.

Reiterating its demand for the resignation of Chidambaram, BJP wanted to know at whose behest was the much-publicised note by the finance ministry prepared?

"At whose instance did the Finance Ministry prepare the note for the PMO?... The country is certainly entitled to know if the PMO had asked for the note. If yes, why was there no follow-up action?" Prasad said.

BJP alleged that even in the case of former telecom minister A Raja, who is now in jail in connection with 2G scam case, the Prime Minister had initially said twice that he is not guilty.

"Is the same story going to repeat itself in the case of P Chidambaram?" Prasad said.

"Skeletons are fighting skeletons and rocking the boat of UPA. How long will you keep quiet, Mr Prime Minister?" Prasad said.

He said the government cannot get away by saying this new development is also due to coalition politics as the "expose" has come from the finance ministry of Pranab Mukherjee who is no. 2 in the cabinet.

"Culpability of Chidambaram is evident," Prasad said.

A finance ministry note to the Prime Minister's Office in March has surfaced, which said Chidambaram could have prevented the spectrum from being given away at throwaway prices.

Prasad said he wanted to ask the "great patrons of Chidambaram" in the government if the minister had abused authority and allowed some persons to "gain pecuniary advantage without public interest".

Prasad also accused the Central Bureau of Investigation (CBI) of double standards in relation to the 2G spectrum probe.

"The CBI is more than keen to question Jaswant Singh (former finance minister) but is absolutely stonewalling pleas to investigate Chidambaram despite voluminous evidence," he said.

Calling upon Prime Minister Manmohan Singh to order a probe, Prasad said not doing so will further tarnish the image of government at a time when there is pressure from people on cases of corruption.

"Is your (PM's) confidence in your colleagues more important, or, a fair, transparent investigation?" Prasad asked, referring to a statement of Manmohan Singh that Chidambaram enjoyed his confidence.

Prasad said that on Nov 22, 2007, then finance secretary D Subbarao wrote to his counterpart in the communications ministry raising concerns that spectrum was being allocated at 2001 prices, and suggested that either current valuation or indexation should be done.

Prasad said Chidambaram wrote a letter on January 15, four days after spectrum allocation, in which he said auction was the correct way of giving spectrum but added that his ministry treats the allocations already made "as a closed chapter."

"If an auction had been done (of 2G spectrum), it would have fetched at least Rs 35,000 crore," Prasad said.

In its March 25 note to the PMO, the finance ministry says Chidambaram could have prevented spectrum from being given away at throwaway prices by insisting on its auction, implying that presumptive losses worth thousands of crores could have thus been avoided.

Sonia Gandhi backs Chidambaram

Meanwhile, Congress chief Sonia Gandhi has directed top leaders to put up a joint defence, party insiders said.

Gandhi, who has recently returned after a surgery abroad, is learnt to have stepped in to resolve the crisis involving one of the government's most high profile ministers.

The opposition has been asking for Chidambaram's resignation and there iis speculation that things are not as they should be between Chidambaram and Pranab Mukherjee.

"Soniaji has asked all top leaders - from Prime Minister Manmohan Singh to party spokespersons - to defend Chidambaram and the government," a senior Congress leader said condition of anonymity.

"She knows that this is an explosive issue. Yesterday it was A Raja and Dayanidhi Maran (ministers who had to quit over the 2G spectrum row), today it is Chidambaram and tomorrow it can be Manmohan Singh. She wants to stop the slide," he added.

Corporate affairs minister M Veerappa Moily's strong defence of Chidambaram on Friday and the home minister's statement that he would not comment on the issue till the Prime Minister returns from his foreign visit are learnt to have been directed by Gandhi.

Though Congress leaders deny talk of a Mukherjee-Chidambaram rift being the root cause behind the controversial note, political analysts and party insiders say there is a "recurring cold war" between the two.

"The rivalry between the two financial wizards has been escalating in the past two years. Soniaji was aware of the issue and had intervened to defuse the situation occasionally," said a Congress leader.

"The cold war has been surfacing through various incidents and on different occasions. A major incident was when Mukherjee confirmed June 22 that he had suspected that his finance ministry offices were bugged in September 2010 and had sought a secret inquiry," said an analyst.

The needle of suspicion then had pointed to intelligence agencies controlled by Chidambaram's home ministry.

Supporters of Mukherjee are believed to have told Gandhi that the veteran leader's trouble-shooting capabilities and political skills were often ignored and "administrative tough actions" advocated by Chidambaram were enforced, leading to fresh crises.

"The latest example was the handling of the fast by civil society leader Anna Hazare in August," said another party leader.

He said Hazare was arrested on August 16 on the direction of Chidambaram, prompting massive protests that led to the activist being released.

The group of ministers led by Chidambaram, who were handling the Hazare fast, was replaced by a team led by Mukherjee and law minister Salman Khurshid. The new team could broker peace and end the 10-day-old fast by Hazare, the Congress leader added.

Kerala-based political analyst B R P Bhaskar told IANS that the Mukherjee-Chidambaram rift may continue till Rahul Gandhi takes a more leading role in the Congress.

"Some infighting had been common in Congress... With a member of the Nehru-Gandhi dynasty usually on the top slot earlier, the fight had been for the second or the third place.

"But now it is different. With Sonia Gandhi recuperating and Rahul Gandhi yet to take over the top post in the party or the government, several leaders and ministers will be working against each other," Bhaskar said over the phone.