New Delhi: Criticizing the Opposition "onslaught" on 'cash-for-votes' scam, Prime Minister Manmohan Singh on Wednesday warned that believing a diplomatic communication was "dangerous".

The Prime Minister adopted a combative approach to the Opposition attack and demands that he should quit in the wake of resurfacing of charges that MPs were purchased to save the UPA-I government.

In an uncharacteristic manner, he particularly targeted L K Advani for raking up the issue, saying the BJP leader thought becoming Prime Minister was his "birth right" and hence had never "forgiven me".

He asked Advani to wait for three-and-a-half years, in an apparent reference to the next Lok Sabha polls, while insisting that nobody from Congress or government was involved or had "authorised" anybody to engage in "transactions" like purchase of MPs during the trust vote.

The swipe was followed by thumping of desks by the Treasury benches and peals of laughter. Congress president Sonia Gandhi and Finance Minister Pranab Mukherjee were seen smiling as was Advani himself.

He also raised questions over the authenticity of the correspondence between the US Embassy here and its government in Washington.

Replying to a short duration debate in both Houses of Parliament over his statement on the WikiLeaks documents which were first accessed by a national daily, Singh said the government could not verify the authenticity of correspondence.

Speaking on the issue in Parliament for the second time since March 18, Singh warned that believing a communication sent by some official in an Embassy was a "dangerous thought".

To press the point that the bribery charges were wrong, Singh referred to the probe by a Parliament's Committee in 2008 and said it had concluded that there was insufficient evidence to prove that MPs were purchased.

"I am convinced that taking the report as a whole, this is a correct inference.... I leave it to the good sense of this House to decide for itself whether the report of the Committee in any way substantiates the wild allegations levelled by some Hon'ble Members of the Opposition," Singh said amid thumping of desks.

Referring to the Opposition attack on him, he said, "This is not for the first time that I have faced in my Parliamentary career the Opposition onslaught of the type we have witnessed of late. I have had to go through that as Finance Minister and as Prime Minister."

Attacking the BJP, he said right from 2004, it had adopted the attitude that "we are a usurper".

Earlier, a united Opposition attacked the Prime Minister, asking how he could wash his hands of the 'cash-for-votes' scam and questioning why he continued to remain in the post if he was unaware of developments involving his government.

Slamming Singh for arguing that 2009 Lok Sabha poll win proved nothing wrong had happened during the Confidence Motion, the Opposition parties, including BJP and Left, said electoral victory cannot condone the criminality of the matter which had "shamed" Indian democracy.

The debate in both the Houses saw frequent clashes between the ruling and opposition benches, with leading lawyers from both sides including Home Minister P Chidambaram,
HRD Minister Kapil Sibal and Parliamentary Affairs Minister Pawan Kumar Bansal batting for the government.

From the Opposition side, BJP leader Arun Jaitley led the fight in Rajya Sabha and Leader of the Opposition Sushma Swaraj in the Lok Sabha.

Sonia’s rare intervention in debate

Congress President Sonia Gandhi, in a rare intervention, sought to dismiss in the Lok
Sabha BJP's charge that the cash-for-vote scam was aimed at salvaging the Indo-US nuclear deal, besides saving the UPA-I government.

"They used to say the same about your government," Gandhi told Yashwant Sinha (BJP) when he said that apart from the government and its longevity, the Indo-US nuclear deal was at stake at the time of the 2008 trust vote.

The one-line intervention by the UPA Chairperson came at a time when Sinha was going all out to attack the government over the WikiLeaks expose.

Gandhi's intervention was loudly cheered by the Treasury benches with Congressmen thumping their desks.

Sibal blames Advani for entire drama

Seeking to turn tables on the BJP on the cash-for-vote scam in the Lok Sabha, HRD Minister Kapil Sibal said that a senior leader from the opposition party had charged L K Advani with being at the "centre" of the entire "drama".

Sibal recalled an interview by senior BJP leader Jaswant Singh to a news magazine in 2009 in which he had blamed BJP Parliamentary Party Chairman L K Advani for being behind the cash-for-vote scam.

The Union Minister quoted from the interview in which Singh had claimed: "Here was a man who was consumed by an ambition to be Prime Minister...Advaniji was at the centre of
this whole drama..."

Sibal also referred to another WikiLeak expose quoting a diplomatic cable in which some BJP leaders had reportedly said that the party's opposition to the Indo-US nuclear deal was
only meant for public consumption.

Accusing BJP of "doublespeak", he said speaking in different languages has been the main opposition party's policy throughout.