New Delhi, Sep 25 (IANS): The BJP's West Bengal unit was completely unaware about former Union Minister Babul Supriyo's plan to exit the party and his sudden joining of the Mamata Banerjee-led Trinamool Congress came as a shock, a party leader said.

The leader said that they did not expect the sudden exit of Supriyo within the three months of being dropped as minister.

"The way Supriyo announced to quit politics in his social media post and later on clarified that he would continue to serve his Lok Sabha constituency, there was a general belief that the former Union Minister will remain in the party. Party leadership had the feeling that he will actively participate in party activities but no one expected that he would leave the party.

"Many senior leaders were in touch with Supriyo and he never hinted that he was going to leave the party," he said.

Another party functionary said that no one thought that Supriyo would join the Trinamool after the BJP named him one of the star campaigners for the West Bengal bypolls.

On July 7, Supriyo was dropped from the Narendra Modi government and soon announced his decision to quit politics. He had also said that he is resigning as MP. On August 2, however, Supriyo, after a meeting with BJP chief J.P. Nadda, had said that he will continue to serve as MP

"I will remain an MP and fulfil my constitutional duties as MP but not participate in politics. I also gave up my official bungalow and central security provided to me. There is politics beyond the constitutional post and I withdraw myself from it. I will not join any other party," he had said after meeting Nadda.

On September 10, the BJP announced Supriyo as one of the star campaigners for the by-polls, but on September 18, he switched parties.