The incident between two cars happened on London Road at around 3.20am today (January 2).
The men were taken to hospital with “serious but not life-changing” injuries, Met Police said.
A driver, aged in his 50s, was arrested on suspicion of drink driving and is in custody.
A second man, aged in his 30s, was also arrested on suspicion of traffic offences and remains in hospital.
London Road remains closed.
A Met Police spokesperson said: “Police were called to a report of a two-car collision on London Road, Thornton Heath at around 3:20hrs on Friday, 2 January.
“Two men were taken to hospital and suffered serious, but not life-changing or life-threatening injuries.
“A man in his 50s, the driver of one of the vehicles, was arrested on suspicion of drink driving and remains in custody.
“Another man, aged in his 30s, was also arrested for traffic offences. He remains in hospital.
“Enquiries are ongoing. If you have any dashcam footage or information that may assist, please contact police on 101, quoting CAD 727/02Jan.”
