Oxford teenager Martha Fernback died after taking drug

Martha Fernback's family said she was "our beautiful girl"

A teenage girl who died after suffering a cardiac arrest in Oxford had taken a drug she believed to be ecstasy, police said.

Martha Fernback, 15, from the Oxford area, is believed to have taken what she thought was MDMA (ecstasy) at Hinksey Park on Saturday.

Her family described her as "effervescent" and "extraordinary".

Police have arrested a 17-year-old male on suspicion of possession with intent to supply a controlled drug.

Det Insp Brendan Murray said: "Following our initial enquiries we now understand Martha had taken a substance earlier that day which she believed was MDMA.

"It would be wrong to speculate on what this substance was or what caused her death, as the investigation is still at an early stage."

In a statement issued by Thames Valley Police her family said: "We are all utterly devastated and have sought such comfort in the beautiful condolences we have received from everyone.

"All her family and friends felt so privileged to have known her."

Martha suffered a cardiac arrest at Hinksey Park near South Oxford Community Centre in Lake Street just after 13:00 BST.

Paramedics were called and she was taken to hospital by air ambulance where she later died.

A post-mortem examination is due to be held on Monday.