A veteran Congressman, Haque had served as MLA from Farakka in West Bengal’s Murshidabad district for five terms. He tendered his resignation on September 21.

In a letter to AICC president Sonia Gandhi on Tuesday, Haque expressed his gratitude to the party and Sonia Gandhi and submitted his resignation from the primary membership of the party.

Mainul mailed his resignation to both Gandhi and West Bengal Congress chief Adhir Ranjan Chowdhury, people aware of the development said.

The senior leader was a Congress observer for Jharkhand. He was also a former observer for Jammu and Kashmir. Haque had discussed his decision to join the Trinamool Congress in July this year.

“After losing the poll, Mainul had shown interest in defection,” said a Congress source.

Reacting to the defection, Leader of Opposition Suvendu Adhikari said Haque was defecting to the ruling Trinamool Congress to get a hiding place from his “malpractices”.

“Coal, sand, bricks, pebbles, etc. are smuggled through Farakka to other states and the former MLA’s inclusion in the Trinamool will help him to continue with his malpractice,” Suvendu alleged.