Sikri's consent was "taken orally for a vacancy" in the Commonwealth tribunal, sources said.
Sources close to the second senior-most judge after the Chief Justice of India Ranjan Gogoi told PTI that the consent was withdrawn Sunday evening when the judge wrote to the Law Ministry, seeking withdrawal of his consent.
"Since this consent was taken in the first week of December 2018, it has no connection with the CBI matter for which he became the CJI's nominee only in January, 2019," the sources added.
They said "a totally unjust controversy" has been raised by connecting the two.
Sikri's vote proved crucial to remove Verma from his post as Kharge opposed the move strongly while the government was pushing for Verma's removal.
On the CSAT issue, the sources said, "It is not an assignment on regular basis. There is no monthly remuneration. There may be two to three hearings in a year. There was no question of staying in London or at any other place."
The government has not got back to him on the CAST assignment, they said.
"The government had approached him for the part-time assignment last month. He gave his consent. The job required attending two to three hearing per year and came without emoluments," the sources said.
Sikri wrote a letter to the competent authority in the government withdrawing his consent.
"He (Justice Sikri) has withdrawn his consent, he has given no reasons. He just wanted to be away from the controversy," a source close to Justice Sikri said.
The source said Justice Sikri "is a man of very simple nature" and he felt that there should not be any controversy over his appointment and that is why he wants to keep himself away from the controversy."
"The Government has a lot of explaining to do (sic)," Patel said in a tweet tagging a media report.
The External Affairs Ministry communicated to CSAT about India's nomination, the sources said.
There was no reaction from either the Ministry of External Affairs or the Ministry of Law and Justice on it.
The Commonwealth Secretariat, established in 1965, plays the role of an arbiter in case of disputes among its 53 member-countries.
The CSAT has a total of eight members, including its president. The members are picked up on the basis of regional representations. A CSAT member has a tenure of four years.