One of Treasury’s most senior executives, Matt Flavel, is no longer working for the department following an internal investigation into his conduct.

The former deputy secretary has started a new role with the Department of Social Services as a group manager for market capability in the disability and carers stream.

Treasury confirmed to Guardian Australia that Flavel, who was on leave from the department’s leadership team late last year during an internal investigation, was no longer an employee.

In an email sent to staff last December, Treasury secretary Steven Kennedy said the department was looking into what he said were “a number of allegations regarding the conduct of a Treasury employee”.

“I am taking appropriate steps to investigate the allegations,” the note said.

Staff at the Department of Social Services were notified of Flavel’s new appointment on Friday by acting secretary Nathan Williamson, and he began the new role this week.

“I want to assure you that we have robust processes and procedures, including independent reviews, to deal with such matters, and these are being closely followed,” Kennedy said.

The email from Kennedy said his “number one priority” was the welfare of staff.

“I want all employees to feel comfortable to raise difficult matters at any time, without fear of any adverse action. I want every Treasury employee to feel safe in the knowledge that these matters will be dealt with sensitively and respectfully.”

The email encouraged staff to take up support through the department’s “wellbeing team” or through an external employee assistance provider, with the assurance that conversations will be treated “in strict confidence”.

Asked about the investigation at the time, Scott Morrison said the department would follow a “proper process” in investigating the allegations.

Flavel was appointed deputy secretary of Treasury’s corporate services and business strategy group in July 2017, and was serving in that role until the final week of October. He had worked at Treasury for 16 years and was previously head of the budget policy division, responsible for the delivery of three federal budgets.