Seth had met Ghosh at BJP's state unit headquarters in Kolkata earlier this week and finalised his joining the party.
A former MP from 1996-2009 from East Midnapore and CPI(M) state committee member, Seth was expelled from CPI(M) for "anti-party activities" in 2014.
After the expulsion, he had floated Bharat Nirman Party but it failed to make any dent in the political space of the state.
The anti-land acquisition movement leaders had alleged his role had caused the flare up of violence culminating in police firing. They also blamed him for atrocities on farmers who refused to part with their land.
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