The high profile SP general secretary and Rajya Sabha member Shahid Siddiqui, who came in support of the Indo-US nuclear deal ever since the UPA-SP tie up, quit the party and announced his decision to join rival BSP.

"For the last one month, I have been feeling uneasy over the nuclear deal. I am of the opinion that it is not in national interest. I have been opposing it for the last three years," he said with UP Chief Minister Mayawati by his side after a meeting with her.

Siddiqui, also a journalist, said that he was taking this position heeding to the call of his conscience and would oppose the deal to the hilt.

SP, which has a strength of 39 Lok Sabha MPs, is already down to 35 with three rebel MPs -- Munawar Hasan, Raj Narain Budholiya and Jai Prakash being joined by S P Baghel.

Though Siddiqui's resignation does not affect Samajwadi Party's numbers in Lok Sabha, it comes as a huge embarrassment to the party that is in the forefront in attempts to muster numbers for the UPA government in the trust vote on Tuesday.