The BJP on Thursday formally lost control over the only civic body it was running in West Bengal, with the Trinamool Congress members passing a no-confidence motion against Bhatpara Municipality Chairman Sourav Singh.

Amid stringent security, the no-confidence motion was passed with a 19-0 margin at a special session of the municipality. None of the BJP councillors attended the session.

However, BJP MP from Barrackpore Arjun Singh later claimed the voting was held in violation of rules. "We will move the Calcutta High Court soon," he said.

On the other hand, the Trinamool leadership said the voting process followed the due process of law.A

After coming out with its most spectacular showing in the state mid last year by capturing 18 of the 42 Lok Saba seats, the BJP retained the momentum capturing one municipality after another as Trinamool councillors crossed over to the BJP in waves.

Bhatpara in North 24 Parganas district opened the floodgate of desertions from the Trinamool ranks to the BJP, days after the party snatched the Barrackpore Lok Sabha seat. Arjun Singh, a former Trinamool MLA known for his muscle power and money power, crossed over to the BJP and pocketed the LS seat by unseating former Union Minister Dinesh Trivedi.

In June, 19 Trinamool councillors had switched their allegiance to the BJP.

The BJP tally had at one time swelled to 26 in the 34-member board.

But the script was reversed soon, as the Trinamool fought back to wrest control of all the seven municipalities which had swing the BJP's way after the LS polls.

In November, the BJP got a huge blow, as 12 of its councillors in Bhatpara municipality returned to the Trinamool Congress, which regained a majority.

The Trinamool win in Thursday's no-confidence motion has only formalised the process.