"Third front will soon become a reality...SP will play a decisive role in its formation.... Without SP third front cannot take shape", Yadav told reporters here.
Replying to a question, Yadav said BJP has "humiliated and sidelined" L K Advani, an architect of the party, which has created dissent in the party cadres.
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"BJP has now lost relevance in political scenario," he said.
About Gujarat Chief Minister Narendra Modi, Yadav said he was "unknown" in Uttar Pradesh and could not affect the prospects of ruling SP.
"BJP wants to project Modi as a national leader but the Modi-card will not work in Uttar Pradesh," he added.
Attacking BSP, he said some former ministers of Mayawati regime were in jail while inquiries were underway against many others in corruption cases and they would also go to jail, if found guilty.
"Mayawati had collected huge commission during her regime through ministers and some officials and no one will be spared if found guilty," he added.