"After stepping down on January 15 as Diamondharbour MP, I will publicly let everyone know in details the reasons and circumstances behind the decision. But I am severing all contacts with TMC," he said at a function here in Hooghly district.
Mitra, who recalled having joined Trinamool during the height of Singur movement, said lack of unfulfilled promises and several incidents in the state prompted him to take the move.
Union minister of state for railways and Baharampur Congress MP Adhir Chowdhury, who was also present at the event held on the occasion of a football tournament, said if someone like Mitra joined Congress, "that will lead to new optimism for Bengal."
Expressing gratitude for Mishra, Chowdhury recalled how in 1996, Mishra, the then WBPCC chief, gave him ticket for Nabagram Lok Sabha seat when the erstwhile CPM government "prevented him from entering Baharampur by initiating a murder case against him."
"Even without my physical presence in Nabagram, I could win with cassettes played during campaigns. Later on, I went on winning thrice from Baharampur," the Congress strongman recalled.
Asked if he had once said Mitra could join Congress only after stepping down from his MP's post, Chowdhury denied having ever said so.
He said with various factions of TMC at loggerhead, Bengal was witnessing unrest on law and order front.
The football tournament was organised by senior state Congress leader Abdul Mannan.