An inquiry has been launched into concerns a couple were left in their car for up to three days after police in Scotland failed to respond to reports of an accident.

It is believed John Yuill, 28, was found dead in the Renault Clio at around 10am on Wednesday after police were called to the crash site near junction nine on the M9. 

The passenger, believed to be 25-year-old Lamara Bell, was taken to hospital in Glasgow in a critical condition. 

The couple were last seen with friends in Loch Earn in the early hours of Sunday.

Police said the pair had been reported missing and that they believe the incident is connected to the search.

Assistant Chief Constable Kate Thomson said officers had been alerted to reports of a car having gone off the road "late on Sunday morning" but did not investigate.

She said: "For reasons currently being investigated, that report was not followed up at the time.

"Officers have notified the families of this update. Our thoughts are with both families at this difficult time.

"A full investigation is currently under way to establish the full circumstances of the incident."

The Police Investigations and Review Commissioner (PIRC) said it is looking into what happened.

A spokesman for the PIRC said: "The Crown Office and Procurator Fiscal Service has directed the Police Investigations and Review Commissioner to carry out an independent investigation into the circumstances surrounding the death of a 28-year-old man and serious injury of a 25-year-old woman following an incident at the M9 southbound near junction nine at Bannockburn on July 8."