Police investigating the death of Peaches Geldof found "importation quality" heroin hidden in her home that was more than double the normal level of purity.
Forensic scientist Dr Peter Cain analysed the brown powder found and concluded that it was 6.91 grams of heroin with a purity of 61%.
Detective Chief Inspector Paul Fotheringham, who led the investigation, told the inquest that the drugs would have been worth £350 to £550.
The officer said that it "far exceeded" the 26% purity usually found at street level.
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The 41-year-old father of six died last Thursday - a week before he and the band had been due to begin touring in North America.