Seeking to turn the table on Kejriwal, the Congress leader said he would also be posing him questions tomorrow.
In a letter to Kejriwal, Singh said "when YP Singh (Retd IPS), your former colleague in civil society movement, called you a Hitler, I could see the streak in you.
"My opinion about you of a well-meaning crusader of public issues has now changed to a self-serving ambitious megalomaniac with scant regard for democracy," he said.
Digvijay Singh claimed Kejriwal couldn't get along with Aruna Roy, who was "your guru in RTI movement. Then you parted ways with Kiran Bedi and now, also with Anna whom you used as a front to give your ambitions a touch of respectability".
He claimed Kejriwal wanted him to recommend his name for being made a member of the National Advisory Council.
"You wanted to meet her (Sonia Gandhi) and had requested me to propose your name for inclusion in the NAC. I did propose your name but failed. She took Aruna Roy," Singh said.
He also said Kejriwal had first met him during a seminar at Berkeley University in San Francisco and that the Congress leader was quite impressed by his commitment to the cause of RTI.
In the letter, Singh also suggested that the "failure" to get in the NAC prompted Kejriwal to upstage NAC in the task on the Lokpal bill.
"I feel this was the time when you made up your mind to upstage NAC by bringing in Anna Hazare and force the government to engage you in drafting the Lokpal Bill," he said.
He prefaced the remarks by saying that a strong Lokpal was the next main item on the Agenda of Congress President.
"She had publicly declared her intent at the AICC session at Burari in December 2010. She entrusted this task to NAC members Aruna Roy and Harsh Mandar and directed them to draft a strong Lokpal Bill," Singh recalled.
"Your draft, if accepted in totality, would have made the Jan Lokpal as the most powerful man in our successful and functional democracy, without being accountable to any one.
"You could have waited for the draft being prepared by Aruna Roy and then suggested amendments, which could have been discussed by all political parties to enable an acceptable draft to emerge and get adopted," Singh said.
The AICC general secretary accused Kejriwal of forcing Anna Hazare to take "my way or the highway" route on Lokpal.
"You are aware of the fractured structure of Parliament and do realize that any legislation in this Parliament can be passed with a consensus only. But you forced Anna to take the route of "my way or the highway" and tried to steamroll the political process only to meet your own whims," Singh said.
Singh noted he was "very happy" that Kejriwal has chosen to form a political party and decided to fight elections as "in a democracy, this is the only way to deliver in public life."
The AICC leader said his only advice to Kejriwal as a senior politician is to "first practice, then preach".
He also reminded Kejriwal that he was "all praise" for Sonia Gandhi on an earlier occassion when he had met the activist along with Swami Agnivesh who had approached the AICC leader for a Conference on RTI.
Singh said it was Sonia Gandhi's political will that ensured the RTI Act that became a reality in India and that how fiercely the establishment had then opposed this law.
The AICC leader said he read in an interview the priorities listed by Kejriwal if he ever came to power, which were the ones which he was already following as Chief Minister of Madha Pradesh and that was the "core policy of Congress".
"Lately, I have been seeing you asking questions to people against whom you are making allegations. Therefore, I also have certain questions to ask to you.
"Would you answer them or dismiss them all in the manner my uncomfortable questions to Sangh, Anna and Ramdev have been dismissed? I would be sending the questions to you tomorrow," Singh said.
He said he placed his list of assets and the assets of his Ministers every year on the table of the House in his tenure as Chief Minister of Madhya Pradesh but the BJP government, which succeeded his, discontinued this practice.
"I have hauled all those who have made charges of corruption against me to the court and they haven't been able to substantiate any charge against me," Singh claimed.
Responding to Singh's allegations in the letter, Kejriwal's close associate Kumar Vishwas told PTI "we have one thing to say. Get well soon."
Digvijay's letter does not merit response: Kejriwal
Activist Arvind Kejriwal tonight said Digvijay Singh's letter describing him as a "self-serving ambitious megalomaniac" does not merit a response and it only showed that Congress party was "completely rattled and baffled".
"Digvijay's letter to me does not merit a response. Congress seems to be completely rattled and baffled. That is apparent from Digvijay's letter.
"Digvijay seems Congress' last resort," Kejriwal, who heads India Against Corruption (IAC), tweeted.
Responding to Singh's remarks, Kejriwal's close associate Kumar Vishwas said, "We have only one thing to say to him. Get well soon."
In a letter to Kejriwal, the AICC General Secretary has described the activist as a "self-serving ambitious megalomaniac" having "streak" of Hitler in him.
Singh alleged that Kejriwal wanted him to recommend his name for being made a member of the National Advisory Council.
What was written is this that Digvijay had recommended him for NAC but his recommendation was not adhere to by congress. What poor standing he has with congress that Digvijay recommendations are not listen too. Whereas Kejriwal seems to be a nationalist who is trying to help government By advising the government. An apolitical person. So I guess he indirectly telling we tried to be friend with him, congress did not follow my advise, we all are crying now.
Digvijay is harming Congress by only attacking anyone and everyone who brings up issue of corruption, as if Corruption is not a huge issue roadblocking India's progress. He has NEVER offered a solution to address the issue and only wants people to stope talking about it. Kejeriwal and Anna on the other hand have proposed a solid plan (draft of Lokpal bill) to deal with issue. People of India are smart enough to see the difference.
How does it matter to you Mr.Digvijaya Singh? You just a few days back was telling the TV interviewer that you are not making any personal comments on anyone. What if Kejriwal want to emerge a strong crusader against corruption irrespective all the inconveniences people like you want to put in his way?