A British mother is demanding to know why an unclassified party drug that killed her daughter has not been banned despite the government acknowledging how dangerous it is.

Hester Stewart from Brighton, East Sussex, died on Sunday morning after going to a party with friends, where she is thought to have used the liquid drug GBL.

Police are investigating whether the 21-year-old, who was studying molecular medicine at Sussex University, took the colourless and odourless drug unknowingly.

Stewart's mother Maryon said she felt "absolutely devastated" that government proposals last August to ban GBL (Gamma Butyrolactone) had not been implemented.

The substance is already illegal in several other countries including the U.S. but is easy to buy online.

"I'm absolutely devastated I've lost my daughter," Maryon Sterart said. "She wasn't the kind of girl who would risk her life."

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