Main contractor Costain has been waiting for the green light on the £260m project since January 2022.
The go-ahead was first delayed to June, and then postponed further until this month.
At the time, the delay was blamed on the need for the Government to give its response to the Sir Peter Hendy Union Connectivity Review.
Now Transport minister Huw Merriman has revealed the decision will be put back by a further 9 months to September 2023.
The announcement is another setback for the contractor, which was originally due to start construction between July and September 2022 and end in 2024/5.
Hopes that the project would finally be started were raised under Liz Truss’s brief tenure as Prime Minister.