Rewati Raman, the 68-year-old Allahabad MP, reached the Crime Branch office in Chanakyapuri at around 11:40 am.
The questioning of Rewati Raman comes three days after his former party colleague Amar Singh was questioned by the investigators. Two persons Sanjeev Saxena, former aide of Amar Singh, and Suhail Hindustani, an alleged go-between Amar Singh and BJP sought to be bribed, were arrested after quizzing.
The aim of questioning is to ask Rewati Raman about the telephone call he received from Hindustani on the midnight of July 21 and 22 to strike a deal to buy BJP MPs, a senior police official said.
Police had already given a virtual clean chit to Rewati Raman and others saying it was Hindustani only who tried to approach them for striking a deal for MPs to vote in favour of the UPA government.
Investigators believe that Hindustani is the "master orchestrator" of the scam and he tried to entrap leaders of Samajwadi Party and it was this purpose that he telephoned Rewati Raman.
Police claimed that none of the Congress leaders or SP leaders mentioned by Hindustani had made any effort to contact him to strike a deal.
Investigators are also preparing to question BJP MP Ashok Argal, who was allegedly given the bribe money, and BJP leader L K Advani's former aide Sudheendra Kulkarni this week before police submit its status report to Supreme Court this Friday.