The BJP central leadership had announced Basu's name as the party's candidate for the byelection Sunday evening. Hours later, Basu told reporters that she is still with the TMC.
"I am a loyal soldier of TMC supremo Mamata Banerjee. I am still with the TMC and have full faith on Mamata Banerjee," Basu said.
Sources in the BJP said Basu had given a missed call to the party's toll-free number to get a membership. There was no official announcement on her joining the saffron party.
The two-time TMC MLA from Noapara assembly seat, however, chose to speak little on the matter and said it was her personal decision to decline the BJP's offer.
"You can have offers from various political parties. But whether you will accept it or not is a personal decision."
Basu, known to be a close associate of Mukul Roy during his stint with the TMC, was seen holding regular talks with the BJP in the past few days after being denied a ticket from the seat by the Mamata Banerjee-led party.
A senior BJP leader claimed that Roy, who had joined the saffron party in November last year, had pitched for Basu even as a section of state BJP leadership was not very keen on giving her the ticket.
A visibly-embarrassed BJP tried to put up a brave face yesterday and accused the ruling party of arm-twisting its candidate.
"We were aware that she was being threatened by the TMC. That's the reason She was forced to backtrack," BJP general secretary Sayantan Basu said.
The TMC has announced the name of Sunil Singh as its candidate from Noapara.
The bypoll has been scheduled for January 29 and counting of votes will take place on February 1.