Kolkata: After a two-and-a-half-hour long grilling by the Central Bureau of Investigation in connection with the Narada TV sting case, BJP leader Mukul Roy on Saturday accused West Bengal Chief Minister Mamata Banerjee of hatching a "big conspiracy" to frame him, but promised to cooperate with the probe agency whenever he gets a call from them. Former Railway Minister Roy, who landed at the federal agency's office in Nizam Palace in south Kolkata at around 2.15 p.m., claimed that he was not involved in the scam.

"I would like to state that I am always ready to face the probe agency, because I know I have no involvement in the case," he said while leaving Nizam Palace. When asked why he was saying so, Roy said: "Yes, I am saying this. Have you seen the footage? Have you seen me taking money from anybody?"

He then made the startling allegation against Banerjee. "Mamata Banerjee is hatching a big conspiracy against me. Whoever is being arrested for corruption, they are being told to take the name of Mukul Roy," he said.

Asked whether IPS officer S.M.H. Mirza, who was arrested by the CBI for his alleged involvement in the Narada scam on Thursday, has been instructed to take his name, Roy said: "Everybody is being instructed (to take my name)."

Before levelling the conspiracy allegation against Banerjee -- his mentor during his long stint with the Trinamool Congress -- Roy also took a dig at the Chief Minister, saying she didn't want people to cooperate with the Central Bureau of Investigation (CBI).

"Mamata Baenrjee says one shouldn't cooperate with the investigative agency. And I say helping and cooperating with the probe agency is the duty of a law abiding citizen. So I would like to say that whenever the probe agency calls me, I will cooperate with them.

"They called me today. They questioned me. If they need me, they will call me again, and I will come," he said. Roy parried a query on whether the sleuths brought him face-to-face with Mirza. "This is an internal affair of the agency. If I say anything, it will be wrong. You please contact the probe agency on this," Roy said.

He also answered in the negative when asked whether the investigators have asked him to come again. The CBI had on Thursday evening issued a notice to Roy, asking him to be present at its Nizam Palace office on Friday. However, the former Trinamool Congress leader wrote back to the agency seeking some time to appear, citing pre-occupation with political programmes.

But the CBI sent him a second notice, summoning him on Saturday. Roy had then told mediapersons that he would be available for questioning after 2.30 p.m. on Saturday. The CBI has apparently decided to summon Roy to cross-check the information provided by IPS officer Mirza, who has been remanded to CBI custody till September 30.

In the sting operation conducted by Narada News chief journalist Mathew Samuel in 2014, the IPS officer and a number of senior Trinamool leaders -- including Roy and former Mayor Sovan Chatterjee, both of whom have since jumped ship to the BJP -- were purportedly seen taking cash or asking for money be deposited elsewhere in return for promising favours to a fictitious company.

The footage was uploaded by the news portal in March 2016, ahead of the West Bengal Assembly elections. Mirza, the first person to be arrested in the case, was heard referring to his closeness with Roy in a footage uploaded by the news portal. Roy, it is said, had asked Samuel to meet Mirza, saying he would be the go-between.

The CBI lodged an FIR in the case on April 17, 2017 after a preliminary inquiry revealed prima facie material for registration of a regular case relating to criminal conspiracy (IPC 120B) and under several provisions of the Prevention of Corruption Act. Roy, who founded the Trinamool along with Banerjee in 1998, was regarded as her closest aide, chief troubleshooter and number one election strategist for over one-and-a-half decade.

Then a rift appeared between the two in 2015 after Roy was quizzed by the CBI in the Saradha ponzi scam case. Banerjee started clipping his wings, but the duo seemingly patched up next year. But the peace proved temporary. Roy ultimately quit the Trinamool and joined the BJP in late 2017.