Sydney Transport Partners’ proposed acquisition of a 51% stake in the A$16.8bn ($12.4bn) WestConnex toll road is set to be further delayed as the Australian Competition and Consumer Commission (ACCC) has extended the review date.

The decision for the review was originally due on 19 July but the scheduled date has now been revised to 6 September.

The extended time frame is expected to enable the Australian competition watchdog to consider various competition issues related to the planned acquisition.

"WestConnex is an unusually large toll road project and we are dealing with unusually complex competition issues that we simply require more time to consider."

ACCC chair Rod Sims said: “WestConnex is an unusually large toll road project and we are dealing with unusually complex competition issues that we simply require more time to consider.”

The ACCC said in a statement on 17 May that the deal could create preliminary competition concerns for future toll road concessions, along with road-on-road competition between WestConnex and Transurban’s existing toll roads.

Sims added: “Since our statement of issues, we have been conducting a thorough analysis of the likely impact on competition from the proposed acquisition.

“We set ourselves a very tight nine-week review period after the statement of issues to meet the state’s sale process timeline. However, this has not been possible, despite our best efforts.

“We continue to have competition concerns, with many complex elements requiring analysis, and we need to get to the bottom of them before we make a decision.”

WestConnex is a partially completed 33km motorway that is intended to connect the western suburbs of Sydney with two of Australia’s major international gateways, namely the city’s airport and the Port Botany.

Transurban is an Australian toll road operator and a consortium member of the Sydney Transport Partners.

The company currently owns seven of the nine toll road concessions in New South Wales (NSW), including the M1, M2, M5 and M7 motorways.