An unperturbed Pranab Mukherjee on Wednesday rubbished the BJP charge of "fabricating" signatures on his letter of resignation from the Kolkata-based Indian Statistical Institute (ISI) even as rival Purno A Sangma and the BJP threatened an extra-poll tactic of election petition to scuttle his undisputable victory in the July 19 Presidential poll to occupy the Rashtrapati Bhawan for the next five years.

After a strategy meeting at Lok Sabha Opposition leader Sushma Swaraj's residence here, Sangma shot off a letter to Returning Officer Dr Vivek K Agnohotri, demanding a copy of his detailed order on Tuesday rejecting his objection to the Congress leader's candidature to enable him to take the legal course.

The BJP on Wednesday reiterated a "forgery" by Mukherjee in the signature on the ISI resignation letter to escape the disqualification from the Presidential election for holding an office of profit. Mukherjee laughed at the charge, asking how can he forge his own signatures. It was up to him how he signs and a signature becomes forged only if he does not authenticate it, Mukherjee said, pointing out that the signatures in two different styles is no forgery or fabrication.

His torment over the resignation letter, however, appears to continue to haunt him as there is no clarity on where the ISI received his resignation he claimed to have submitted on June 20 as ISI Director Bimal Roy in Kolkata has been reiterating since the controversy raked up that the resignation was received in his office on June 20 as the chairman of the governing council.

The documents filed by Mukherjee's agents before the Returning Officer on Tuesday, however, shows that it was received by the institute's President Dr MGK Menon, who acknowledges it on a copy as "accepted" with his signatures and date (June 20). Prof. Menon is Delhi based and inquiries show he was in Delhi on June 20 and hence moot question arises as to where the resignation letter was submitted -- in Kolkata with the ISI office or in Delhi with Menon.

The BJP leaders said they were also not sure if Prof. Menon had really signed the acceptance on the copy of the resignation letter filed before the Returning Officer. In normal course, Mukherjee should have sent his resignation to the ISI in Kolkata, but he sending it to Menon in Delhi creates suspicion that it may be back-dated, leaders attending the strategy meeting as Sushma's residence said.

In his letter to the Returning Officer, Sangma sought the detailed order by 5 PM, pointing out that more than 24 hours have passed and he was being deprived of the legal remedy by not giving him a copy of the order.

While Sangma's polling agent and senior BJP leader S S Ahluwalia said the next course of action will be decided after studying the order, his counsel and former BJP MP Satyapal Jain, who argued before the Returning Officer, jumped the gun saying he has the option to move an election petition before the Supreme Court. Accusing the UPA of "lowering the dignity" of the post of President, Jain told reporters in Chandigarh that "election petition is the only remedy once the results are declared."

Home minister P Chidambaram accused the BJP of sullying the Presidential election with "scandalous" allegations against Mukherjee. "It is a scandalous suggestion and I am sure Mr Pranab Mukherjee, the candidate, has taken note of this scandalous statement," he said at a press conference called to announce the Cabinet decisions taken Tuesday evening.