The Kerala Congress (B) of former Minister R Balakrishna Pillai has left the ruling UDF for all practical purposes following a series of serious differences with front leader Congress, particularly Chief Minister Oommen Chandy, and some other constituents. Pillai, one of the founder leaders of the UDF, announced on Wednesday that his son and the party's lone MlA, KB Ganesh Kumar, would vote for Aisha Potti, candidate of the CPI(M)-led Opposition lDF, in the election of the Assembly Speaker on Thursday. The election was necessitated by the death of Speaker G Karthikeyan of the Congress on March 7.