"If you have documents to prove your allegations, bring them to court," Mr Shah said, emphasizing that none of his son's companies "did even one rupee worth of business" with the government or "received kickbacks like in the case of Bofors".
Jay Shah has sued news website The Wire for 100 crores for reporting that his firm's revenues escalated by 16,000 times after the BJP came to power. The report also questioned allegedly unsecured loans given to Jay Shah's firms, including from a state-run firm that reports to the Power Ministry.
NDTV cannot independently verify the allegations, which, according to the Congress, is an "excellent example" of crony capitalism.
"Please understand this is not corruption. Many allegations of corruption were made against the Congress. Did it ever file a civil suit or defamation suit? No. Why they lacked such courage? Today Jay has filed a defamation as well as civil suit and is demanding a probe himself," Mr Shah stressed, responding to questions.
He added: "The business was of commodity trade which is a high value low profit venture. If a company's turnover becomes Rs 1 crore, its profit does not become Rs 1 crore...It is unfair to say there was an over 16,000 times jump in profit...say what the turnover was...It makes it seem like the turnover was huge but it wasn't."
The BJP president also said after achieving a turnover of Rs 80 crore, his son's company suffered a loss of Rs 1.5 crore. "All the payments were made through cheques. There is no question of money laundering." The loans, he said, were not unsecured but a line of credit.
On Thursday, the BJP's ideological mentor Rashtriya Swayamsevak Sangh (RSS) said there must be enough evidence for the allegations to be worth investigating.