The department had awarded a tender to a company which had not fulfilled all the necessary requirements, and overpaid for services by R10 million, it said in a statement.

Global Interface Consultancy won a tender to manage conference and communication services for the Department of Transport's international investor conference in June last year.

It had submitted a bid for R13.5 million.

Losing bidder Indigo Design and Event Marketing bid R3.837 million --about one-quarter of the winning bid.

Indigo Design, a BEE-accredited company, lodged complaints with the department, the Public Protector and Corruption Watch (CW).

"CW’s further investigation into the DOT tender award revealed gross irregularities in the tender process," Corruption Watch said.

Corruption Watch had handed over its findings, as well as two cases involving irregular public tenders, to the Public Protector for further investigation.

It was in the process of formalising a working relationship with the Protector.

"We will closely monitor the cases that we hand over to the Public Protector and we will assist her office with further evidence and information gathered from the public," said executive director David Lewis.

"It should be stressed that this case and each of the serious acts of corruption that we are investigating were reported by alert members of the public."

Comment from the department could not be immediately obtained.