Police warning on 'legal highs' at work A survey of Welsh employers has found one in three do not know how to tell if their workers are under the influence of recreational drugs. It comes amid growing concern about the level of new-style drugs and so-called legal highs across Wales. Police chiefs and drugs agencies have been worried about the rise in the use of mephedrone in Wales. Det Ch Insp Martin Tavener has just retired as head of the regional crime unit. He told BBC Wales economics correspondent Sarah Dickins the drug had become a particular issue in Wales and was used by workers across a whole range of occupations.