The election was necessitated following the death of former Speaker and Congress leader G Karthikeyan.
The result is very important for the UDF government headed by Chief Minister Oommen Chandy, which has been hit by the solar and bar bribe scams and alleged corruptions in the PWD ministry.
For the UDF government, which came to power by a wafer- thin majority of two MLAs in 2011 on the slogan of development and care, a win will be widely considered a referendum on it's performance.
CPI(M) has narrowed its choice down to senior leader and former Speaker M Vijayakumar and an official announcement will be made after approval by the party's state secretariat.
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A measure of how seriously CPI(M) views the bypoll can be gauged from the fact that party veteran and former state secretary Pinarayi Vijayan is in-charge of the poll campaign.
For Congress, retaining the seat is vital as Karthikeyan represented it five times in the Assembly. He won the seat last time by over 10,000 votes, defeating the RSP candiate.
Congress is looking for a suitable candidate to take on Vijayakumar, a popular political personality and most partymen are in favour of fielding M T Sulekha, a teacher by profession and wife of Karthikeyan.
The BJP, trying to make a political breakthrough in the state, is also all set to take on both fronts. Party cadres are upbeat after the increase in its vote percentage in the last Lok Sabha polls and the recent visit of party President Amit Shah.
Winning the poll is crucial for Congress and UDF and all the more for Chandy. A defeat might strengthen the move from a section in the party for a leadership change as part of 'image build up of the government', observers pointed out.
UDF, which came to power with 72 seats and LDF with 68 in 2011, have seen changes in its partners. Kerala Congress (B), led by R Balakrishna Pillai with lone MLA K B Ganeshkumar snapped its ties with the front.
RSP, with two MLAs came to the UDF camp after severing its decades long association with LDF during the eve of the last Lok Sabha polls in a dispute on seat sharing.
UDF now has 73 members and LDF 65 in the 140 member Assembly. Ganeshkumar has kept away from both fronts and one seat of former Speaker is vacant.