Advani alleged that Singh is unable to avail the authority innate to his office due to his "weakness" and lauded Atal Behari Vajpayee as the "most outstanding" of all Prime Ministers the country ever had.
"When in 2009 I had described Dr Singh as the weakest Prime Minister the country has had, some of my own colleagues felt that I was being too severe. But I still hold that it is this attribute of his weakness - that makes him so subservient to 10, Janpath, and thus unable to avail the authority innate in this office of Prime Ministership," Advani said on his blog.
He said due to this "shortcoming" of Singh, history will record that "while personally he may be upright, the Government over which he has presided for a decade has been the most corrupt in Free India."
The BJP leader said this was not just based on media reports but is sustained by several judicial verdicts and numerous reports of the Comptroller and Auditor General.
Advani said though it was a "unique distinction" for Singh to be Prime Minister for almost a decade despite being a person from outside the Nehru family, what was even more unique was his "dubious distinction" of being the only Prime Minster to occupy the exalted office without ever being elected to the Lok Sabha.
Listing various achievements of Vajpayee's tenure, Advani said he did not find "even a trace of ego or arrogance" in him and described him as the 'most outstanding' Prime Minister.
He criticised Prime Ministers Jawaharlal Nehru and Indira Gandhi, who ruled the nation longest, for India's 'ignominous' defeat at the hands of China in 1962 and imposing Emergency, but said they left the greatest impact on the minds of people.
"But if a balance sheet of their plus and minus points were to be drawn up, the net result may not be very flattering," the BJP veteran said. In contrast to these two, the BJP veteran appreciated Lal Bahadur Shastri and Morarji Desai who left a deep impression on people and earned abiding respect among the masses.