The BBC has been shown footage filmed inside a laboratory in China that makes so-called "legal highs".

The sale, distribution and manufacture of the drugs was banned in the UK in 2016 as many of them were found to have lethal side effects.

But Radio 4's File on Four programme managed to order a small sample of a legal high from an online supplier in China.

The drug was posted to the UK concealed inside a plastic container designed to hold a water softener.