SafeWork SA has apologised over a failed prosecution.

Two women were crushed by a steel construction gate in Adelaide's CBD in 2016, when the gate came out of its restraints and fell on top of them as they were walking past.

The two-year statute of limitations on prosecutions has now lapsed, meaning the regulator will not prosecute the site's manager Lendlease.

SafeWork SA executive director Martyn Campbell said the regulator did not secure evidence that could have resulted in charges being laid.

“This incident was done in a time that wasn't great in the history of SafeWork and we should have done better,” he told reporters.

“We should have done better in our initial response in securing evidence. That didn't happen. It won't happen again.”

Mr Campbell said the women injured in the accident have received an apology.

“I extend my sympathy to those people that they won't have their day in court. But that said, they understand the decision and the reason for that,” he said.

“I understand this is a very disappointing outcome for them; I am equally disappointed.”

It is the latest in a series of bungles for the safety regulator, which have led the state’s Independent Commission Against Corruption, Bruce Lander QC, to launch a public inquiry to the regulatory arm of SafeWork SA.