The scale of drug abuse inside jail has been revealed as figures showed one in six inmates in some prisons have tested positive for opiates such as heroin.

Government figures show the highest level of opiate abuse - 16.7% of inmates - was uncovered in random tests at Featherstone prison, Wolverhampton.

The Ministry of Justice added that out of 139 prisons in England and Wales, only 38 were clear of positive tests.