Government scientists are being sent to the V Festival to analyse samples of so-called legal highs amid renewed warnings against taking the party drugs.
The Home Office is launching a national campaign highlighting the risks of legal highs including laughing gas, which was more widely used than powdered cocaine and ecstasy last year.
They are aiming to gather information about which new substances are available in the UK, and the latest Home Office annual report on the trends is due to be published today.
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The families of all four of the victims, all of whom were men, have been informed, police said.
A motorcyclist from Nottingham has died in an accident at the Macau Grand Prix in China, earlier today.
AC/DC co-founder and ex-guitarist Malcolm Young has died aged 64, his publicist has announced.