The alliance between the Trinamool Congress and the Congress, which yielded rich dividends during the Lok Sabha elections, came under strain on Thursday after the Congress mayoral candidate for the Siliguri Municipal Corporation (SMC) was elected with the support of the Left Front.

The TMC-Congress combine had wrested 29 of the 47 seats in the SMC elections held on September 13. While the Congress won 15 seats, TMC won 14. The Left Front won 17 seats (15 by the CPI(M) alone). One seat went to an independent. The Left Front had 36 seats in the outgoing body and had held the SMC board since the eighties.

The poll results were seen as a major milestone in the growing influence of the TMC-Congress alliance all over the State.

TMC chairperson Mamata Banerjee described Thursday’s development as an “unholy nexus,” which would ultimately strengthen her party. “I will personally go to Siliguri within the next seven days and apologise to the people for not being able to give them an alternative despite getting their poll mandate,” she told a private television channel from New Delhi.

“We know the limitations of such alliances in politics and will serve the people while sitting in the Opposition,” Ms. Banerjee said. She would not take up the matter with the West Bengal Pradesh Congress chief Pranab Mukherjee. “But this is a major incident, as it involves bypassing people’s verdict,” she said.

Working president of the WBPCC Pradip Bhattacharjee told The Hindu that the alliance would not suffer as this was a regional issue. He was confident that the prospects of the alliance for the 2011 Assembly elections would not be affected. Subrata Mukherjee, another working president, said that the alliance was the outcome of a mutual need.

Ms. Banerjee, however, said that future steps would have to be discussed. She was replying to a question whether the alliance would be intact for the coming by-elections to 10 Assembly seats in the State next month.

Ashok Bhattacharyya, West Bengal Urban Development Minister and convenor of the Darjeeling district Zilla Left Front, said that the decision to support the Congress was taken to impart some stability in the region that was rocked by the Gorkha Janmukti agitation.