In a major blow to the TMC amid the political turmoil rocking the organisation, Rajya Sabha MP Sukhen Shekhar Ray on Monday resigned from the party and also stepped down as a member of the Upper House of Parliament.

Ray, a veteran leader and one of the most articulate voices of the TMC in Parliament, submitted his resignation to the Rajya Sabha chairman and simultaneously announced his decision to quit the Mamata Banerjee-led party.

The development comes at a time when the TMC is grappling with an unprecedented internal crisis, following a rebellion in its legislative wing and growing tensions among different factions within the organisation.

In his resignation letter, Ray said he was relinquishing his parliamentary membership and severing association with the TMC.

In a statement made to ANI, he said that power had gone to TMC members' heads, to an extent they believed no one could touch them. "Power had gone to their heads to such an extent that they believed no one in the world could touch them. But the very people who sent them there have now brought them down," he said.

Referring to the R G Kar rape-murder case, he said that the leaders did not engage in any discussion about it.

"As soon as the RG Kar incident occurred, the public poured onto the streets. People who had never in their lives joined a procession or a public meeting, and who had no connection to politics, even they, including doctors, stayed out on the streets all night long," he noted.

"I had publicly spoken out on the RG Kar hospital issue. Since then, I was increasingly isolated within the party. My only fault was that I demanded an internal inquiry against certain police officers because I believed they had a major role in destruction of evidence," Ray told reporters in Delhi.

Ray alleged that efforts were being made at the time to shield those responsible, and said he had mentally decided to leave the party soon after the controversy.

"That was the turning point. I realised I would not remain in the party for long," he said.

"At that time, the leaders and administrators did not engage in any deliberation or discussion about it," he added.

The TMC's tally in the Rajya Sabha came down to 12 with Ray's resignation.

Ray, a constitutional expert, has for years been one of the TMC's principal strategists in Parliament and among its most effective voices on legislative and constitutional issues.

Asked about his future plans, Ray said he had not taken any decision about joining another political party, and indicated that he might even retire from active politics.

"I may withdraw from politics altogether," he said.

The TMC leadership did not immediately react to Ray's resignation.

With the rebellion in the legislature wing still unresolved, Ray's departure is likely to deepen questions over the TMC's internal cohesion, and raise fresh concerns within the leadership about whether the unrest that rattled its assembly ranks could eventually spread to Delhi as well.