WA Premier Colin Barnett has said former treasurer Troy Buswell is unlikely to return to Parliament until May.

Buswell took a leave of absence in March after suffering what has been described as a breakdown.

The former treasurer was on his way home from a wedding reception early one morning in February when he allegedly crashed into four cars and a pole in Subiaco.

Hours before reports of the incident began to emerge, Buswell called the Premier and resigned from Cabinet.

Police have charged the former treasurer with 11 driving offences, including careless driving.

The Premier said he thought Buswell would gradually recover and resume full duties.

"I don't think Troy will come back at the end of this week," he said.

"It's more likely to be May. I spoke to him, his health is improving. He's not doing nothing - he's going into his local electorate office and doing electoral work two or three hours a day."

Mr Barnett has refused to comment on the charges against his colleague while the Opposition has called for an inquiry into who knew what about the incidents.

It has repeatedly asked what senior staffers in Government knew about the incident before it came to light.

An internal investigation has cleared government staffers of any wrongdoing but the Premier has not committed to publicly releasing the report.