Calcutta, June 7: Back home from negotiating the diplomatic rapids of Dhaka, Mamata Banerjee faces an unlikely test: how to bring back on board a reluctant former right-hand man who had walked out over "irreconcilable differences".

Ratan Mukherjee, now in his early 60s, had been Mamata's political aide since she became a parliamentarian in 1984. He served her in Delhi and Calcutta as she juggled her roles of Congress MP, Trinamul Congress chief, Union minister in Congress, NDA and UPA governments, and Bengal chief minister.

Mukherjee, however, left Calcutta and the chief minister's office (CMO) following an alleged spat with Mamata in 2012.

Sources close to the chief minister said she had got in touch with Mukherjee about a month ago and asked him to return. "Didi has spoken to Ratanda as she is very keen to have him in Nabanna as her political aide," a source said.

He said Mamata's outreach came after the death of the 57-year-old Ashok Subramaniam, a key CMO official, in April this year.

Subramaniam and Gautam Sanyal, two central secretariat service officers, had accompanied Mukherjee from Delhi to the Writers' Buildings when Mamata quit as railway minister to head the Bengal government in May 2011.

"Like Ratanda, Subramaniam was among Didi's trusted few and handled both the administrative and political sides of her responsibilities. After his death, Didi needs someone equally trustworthy to fill that void," a Trinamul source said.

Mukherjee confirmed that Mamata had got in touch with him. "Yes, it is true that she has reached out to me," he told The Telegraph from Delhi on Friday night.

"I had come down to Calcutta last month for four or five days and met her at Nabanna. But I told her clearly that it's no longer possible for me, after this gap of three years, to return to working 365 days a year."

He added: "I have clearly said no, but she isn't willing to listen. She has requested me to think things over, but I'm unlikely to change my mind."

Mukherjee said he had told Mamata he could at best come down to Calcutta for five or six days a month and help her but was no longer physically capable of shifting base from Delhi.

He explained why he had quit Mamata's service: "I had to leave because of some irreconcilable differences. There was unnecessary friction, and I'm a peace-loving man. When I was given charge in Calcutta, I had assumed I would be given the same authority I had enjoyed for years before that and would be taken seriously.

"But she wouldn't take my suggestions or heed my advice, or even accept hard facts. There came a point when I decided to give up. I have not regretted it since."

Mukherjee, however, said his personal relations with Mamata never suffered even after his resignation.

"Whenever she comes to Delhi, she still calls me and I take my car to be her designated driver for the entire duration of her stay," he said. "She doesn't trust anyone the way she trusts me, at least in Delhi. I will happily be her driver in Delhi for the rest of my life. But that's about it."

Old-timers said it was Bengal panchayat minister Subrata Mukherjee who had introduced Mamata to Ratan Mukherjee, then a Supreme Court clerk in Delhi, in 1984.

"Subratada and Ratanda are close friends. When Didi became an MP for the first time, Subratada brought him along to help her in Delhi. Since then Ratanda had been by her side through thick and thin - until 2012," a Trinamul senior said.

Party insiders said Ratan Mukherjee had been unhappy at what he saw as then Trinamul all-India general secretary Mukul Roy's "interference" in the day-to-day functioning of the CMO and the state secretariat.

Roy not only controlled the party organisation at the time but had a big say in administrative affairs, including police matters. A senior cabinet minister said that Mukherjee had put his foot down over this, unlike some of his colleagues, but Mamata wouldn't listen to him.

Now that Roy has fallen from grace and Mamata has herself been handling the organisation with the help of nephew Abhishek and some others, she felt she could approach Mukherjee with the promise of a changed work environment, the minister said.

"She still trusts him a lot. When she vacated Roy's flat in Delhi in February, Ratanda personally took out her belongings," the minister said.