Police issued a statement, saying, "At this early stage it is being treated as unexplained and there have been no arrests in connection with the incident."
TMZ reported yesterday ... a source connected with the death investigation told us police were "operating under the suspicion" it was an overdose.
Scotland Yard also said, "Police were called by London Ambulance Service to a house in Camden Square NW1 shortly before 16.05 hours on Saturday 23 July, following reports of a woman found deceased."
And as we reported yesterday, we were told when paramedics arrived there were "signs of life," though we did not have specifics.
Now the post-mortem is scheduled for Monday morning.
TMZ caught up with "American Idol" honcho Nigel Lythgoe who called Amy's passing "tragic."