The CBI is likely to file the charge sheet by September 20, sources said.

Former Union Minister P Chidambaram, who was in the custody of the Central Bureau of Investigation in connection with the INX Media case, answered around 450 questions during 90 hours of gruelling interrogation last week, sources told NDTV. Most of the questions were related to the Foreign Investment Promotion Board (FIPB) clearances that the former Finance Minister allegedly secured for the company and his son Karti Chidambaram's alleged mail exchanges with the co-accused in the case.

The CBI alleges that as finance minister in 2007, Mr Chidambaram facilitated a huge infusion of overseas funds to the media company INX Media co-founded by Peter and Indrani Mukerjea, at the instance of his son Karti Chidambaram, who allegedly received kickbacks.

While in custody, sources say, Mr Chidambaram was confronted with five other accused and witnesses. He, however, was not confronted with D Subbarao, who was the FIPB chief when the INX media's proposal for foreign funds was cleared.

The CBI is likely to file the charge sheet by September 20, sources said.

Mr Chidambaram, who was in CBI custody for the last two weeks, was sent to Tihar jail on Thursday by a Delhi court. The senior leader told the court that he was ready to go to the custody of the Enforcement Directorate, following the Supreme Court's refusal to give him protection from arrest by the agency. But the offer was turned down by the judge.

Mr Chidambaram's anticipatory bail plea in the Aircel-Maxis deal case was accepted by a second special court. The former minister's son Karti Chidambaram, who has also been named in the case, was granted protection from arrest as well.

Mr Chidambaram was sent to the Tihar jail where he will be lodged in cell number 5 of ward number 02. He will remain in the jail at least till September 19. The senior Congress leader's lawyer and party colleague Kapil Sibal requested a separate cell for him, a cot, a western toilet and medicines, which were granted as he has Z-security.