A post-mortem on Natasha Collins, fiancee of TV presenter Mark Speight, was "inconclusive" and further toxicology tests will now take place, the Metropolitan Police said yesterday.
In a statement, Scotland Yard said: "The post-mortem examination was held at St Thomas' Hospital today and the cause of death remains unknown.
"We await further test results, including toxicology. An inquest will be opened and adjourned at Westminster Coroner's Court tomorrow."
It was reported that Miss Collins had taken cocaine before her death.
But Speight's mother, Jacqueline, said she may have died after taking drugs prescribed for a medical condition.
Prior to the post-mortem examination, Scotland Yard detectives said a suspected drug overdose was one line of inquiry in the unexplained death.
Miss Collins was hit by a car about seven years ago and reports said she had suffered regular fits ever since.
After her body was discovered, Speight, originally from Wolverhampton, was arrested on suspicion of murder and supplying class A drugs. He has been bailed by police until early February. He insisted he had nothing to do with his fiancee's death.
A spokeswoman for the SMart presenter said: "Mark was the only other person present in the flat and has therefore been questioned by police as a matter of course.
"He is assisting police with their inquiries and had nothing to do with Natasha's death."
Speight is best known for the BBC children's art show SMart, which has run for more than 10 years.
He shot to fame as the rubber-faced presenter of Children's ITV Saturday morning show Scratchy & Co. Miss Collins starred alongside him on BBC children's show See It Saw It.
The BBC has cancelled Saturday's scheduled showing of SMart but has not yet made a decision on whether next week's episodes will be screened.
A new series of SMart is not scheduled until the end of the year.