HALIFAX -- Nova Scotia Premier Stephen McNeil is backing his chief of staff despite learning that she didn't tell him last May about a drunk driving allegation involving a Liberal backbencher.

McNeil told reporters on Thursday that he isn't asking for Laurie Graham's resignation over her handling of inquiries into Hugh MacKay, who resigned from the party's caucus on Sunday and faces a charge of impaired operation of a motor vehicle in connection with a Nov. 22, 2018 incident.

"I continue to have all confidence in her, and I support the judgment she made on this one," said McNeil, who has said Graham first revealed to him her knowledge of the allegation on Tuesday.

He said Graham learned of the allegation by phone when she was accompanying him on a trade mission to Europe last May.

McNeil said Graham spoke to MacKay and to his constituency assistant about the allegation and determined that there was no "basis or foundation" to it.

"She asked Mr. MacKay, was there anything to that (allegation) at that moment in time, and he said absolutely not."

The premier said he doesn't know whether Graham was aware of a May 6, 2019 email containing an allegation about an impaired driving incident involving MacKay from an eyewitness.

The allegations in the email, which the Tories obtained and made public, have not been proven in court.

McNeil was asked whether Graham should have dug deeper into the allegation.

"There's no evidence at all that there was any merit to this," he said. "What should have happened is the person who actually penned the letter should have gone to police on that day."

Progressive Conservative Leader Tim Houston said Graham didn't do enough to delve into an allegation that was serious in nature.

"There's a number of steps that any reasonable person would take .... One of them would certainly include reaching out to the person who wrote the email," he said.

Houston stopped short of calling for Graham's resignation saying it was for the "premier and his chief of staff to determine."

NDP Leader Gary Burrill said he isn't satisfied that the premier's office handled the situation appropriately.

"I think it is an incomplete effort on the evidence that we have seen so far," Burrill said.

MacKay, who pleaded guilty to a separate impaired driving charge last fall and was fined, hasn't been in the legislature this week, and a message left at his constituency office was not returned.

He is scheduled to appear in a Halifax court on March 16.

This report by The Canadian Press was first published Feb. 27, 2020.