Britain's Gambling Commission has already been reported to be investigating two Conservative election candidates and the party's director of campaigning over bets on the date of the July 4 election.
The widening scandal has further damaged Sunak's attempts to catch the opposition Labour Party, which is far ahead in opinion polls in the run-up to the election.
The official was named by the paper as Nick Mason, chief data officer at the Conservative Party. Mason did not immediately respond to a request for comment. The newspaper cited a spokesperson for Mason as saying he denied any wrongdoing.
The Sunday Times cited a statement from the Conservative Party as saying Mason had taken a leave of absence. The party did not confirm this when contacted by Reuters.
"As instructed by the Gambling Commission, we are not permitted to discuss any matters related to any investigation with the subject or any other persons,” a Conservative Party spokesman said.
The Gambling Commission has not confirmed the names of those under investigation. In a response to a request for comment on the Sunday Times report, a commission spokesperson said it would not provide details of its probe, including the identity of any individuals it is investigating.
Sunak said on Thursday he was "incredibly angry" to hear about the allegations against his party colleagues, calling them a "really serious matter."
One of the Conservative candidates named in the scandal, Craig Williams, has already apologised for an error of judgment, and the party's director of campaigning Tony Lee has taken a leave of absence.
A police officer working in a special protection unit has also been arrested over alleged bets on the election date.
