Calcutta, June 12: If cold statistics guide the Trinamul Congress and the Congress in the Durgapur I Assembly seat for the July 5 bypoll, both will realise that a united fight is the best bet to crack the fortress that has stayed with the CPM for decades.

The results of elections over the recent years suggest that if an Opposition alliance has to achieve critical mass, both the Congress and Trinamul should be part of such a combine.

In the 2009 Lok Sabha polls, when the “winds of change” roared across Bengal, the Congress and Trinamul had together polled 41 per cent of the votes in the Assembly segment. The Left was still ahead with 50.5 per cent but the Opposition alliance had managed to bite off as much as 10 per cent of the vote share from the ruling rival, compared with the 2006 Assembly election count. (See chart)

In the 2006 Assembly polls, there were two crucial differences. One, the “winds of change” had not yet started blowing in the state. Two, Trinamul had then allied with the BJP.

The Trinamul-BJP combine then ended up with 15 per cent, while the Congress pulled ahead of the alliance with a little over 20 per cent. If the SUCI’s votes are also included, the combined Opposition’s share in 2006 was less than 39 per cent. However, by 2009, the non-BJP Opposition alone could clock 41 per cent, suggesting that “the winds of change” and the Congress-Trinamul alliance complemented each other well.

If the lessons of the recent civic elections are also taken into account — Durgapur did not have corporation polls last month but several other civic bodies in Burdwan did — they support the need for an alliance between the Congress and Trinamul. In several Burdwan territories where the Congress and Trinamul had unofficial alliances, they gave the Left a run for its money.

“The civic poll results in Burdwan underline the need for a joint fight in Durgapur I,” state Congress working president Pradip Bhattacharya said.

It’s not yet clear, though, whether the Assembly seat will have a Trinamul or a Congress candidate if the two parties re-establish ties.

Trinamul MP and central minister Mukul Roy said the decision was yet to be taken. “Let us see which party contests.’’

The Durgapur I Assembly seat fell vacant in February after the death of its MLA, power minister Mrinal Banerjee of the CPM.

A CPM state committee leader admitted that the party would find it difficult to win the by-election if the Congress and Trinamul stitched an alliance. “It could be difficult if there is an Opposition alliance. We won the last Lok Sabha polls here with a diminished margin. We are trying our best to retain Mrinalda’s fort,’’ the CPM leader said.