Police believe a car may have been travelling the wrong direction on a motorway when it was involved a crash which killed two people.
An 82-year-old man from Swindon driving a blue Mazda 323 died at the scene of the crash between junctions 14 and 13 on the eastbound carriageway of the M4 at 10.34pm yesterday, Thames Valley Police said.
His elderly female passenger was taken to the John Radcliffe Hospital in Oxford and is in a critical condition, a force spokesman said.
A 48-year-old-man, also from Swindon, who was driving a blue Volkswagen Passat, was taken to the same hospital where he died shortly before 5am today, he added.
Sergeant Dick Thorpe, leading the investigation, said: "At this stage we are investigating the possibility that one of the vehicles was travelling in the wrong direction against the flow of the eastbound traffic.
"I am keen to hear from anyone who was on the M4 at this time and witnessed the collision, or who saw a vehicle travelling in the wrong direction."
Anyone with any information should call the Road Death Investigation Unit on 101, or Crimestoppers, anonymously, on 0800 555111.