The Independent Police Complaints Commission is to look into an incident in which a woman was found collapsed outside Aylesbury Police Station just hours after being released on bail.
The 30-year-old woman was taken into custody at the station after being arrested on suspicion of being drunk and disorderly in the town at 10.45am on Wednesday morning.
She was released on bail at 9.23pm later that day but just four hours later – at 1.24am on Thursday – she was found collapsed in the grounds of the police station.
She was subsequently taken to Stoke Mandeville Hospital where her condition is described as stable.
Thames Valley Police has undertaken a mandatory referral to the IPCC because the woman had recent contact with the force.