Buswell's adviser interviewed by WA police

The chief of staff of disgraced former West Australian treasurer Troy Buswell has been interviewed by police investigating the car crash that led to his resignation.

Mr Buswell stepped down from cabinet this week following revelations he was hospitalised for 10 days after a mental breakdown in the wake of a car crash in the early hours of February 23.

He had been at a wedding reception.

Police continue to probe the events that led to Mr Buswell's car crashing into the gates of his own house, and are also investigating damage to other cars and property in Subiaco.

Rachel Turnseck was at the same wedding, leaving several hours before Mr Buswell's fateful journey home.

Premier Colin Barnett confirmed on Friday that she had been interviewed by police.

WA opposition leader Mark McGowan is demanding a public inquiry into the events to find out whether the government had covered up a crime.

"Driving a vehicle while extremely intoxicated is inexcusable under any circumstances. Covering up incidents around that is inexcusable under any circumstances," Mr McGowan said.

"I don't believe the excuses that are being given and there is significant evidence that needs an inquiry."