Cardiff jail is among the most overcrowded in Britain

When inspectors visited Cardiff six months ago they found the Victorian prison held 150 more prisoners than it should.

And although 87% of inmates have been involved with drugs, either as users or dealers, there are no specific detox or rehabilitation facilities.

But preparations are under way to address the problem and the Welsh assembly has provided money for a 60-bed treatment unit.

Chief Inspector of Prisons Anne Owers said: "Local prisons like Cardiff hold a huge variety of prisoners - but some are held for quite a long time - even prisoners who are on remand awaiting trial can spend weeks or months in prison before that happens.

"It is trying to make sure things happen to them within the prison which means they don't just return as soon as they have gone out again.

"Drug detoxification and treatment work is critical to that as well."

Reacting to the report on Tuesday, Cardiff Prison Governor Paul Tidball said it was keeping drugs out of the prison that was one of the main problems.

"The most common way for drugs to be smuggled into prisons in this country is through visits," he said.

"In British prisons, most prisoners are able to embrace and have some close contact with their visitors so it is about the balance between decency and security and we don't, as in the movies, stick people behind glass screens so they can touch each other through the glass."

Cardiff's city centre prison has cramped conditions

According to the report, published on Tuesday, the majority of prisoners - a total of 87% - felt reasonably safe at Cardiff and suicide prevention and care were also commended.

Even so, the study concluded that more education facilities, and more workshops needed to be in place as only 63% of prisoners benefited from access to a purposeful activity.

In a separate report by the Prison Reform Trust last month, Cardiff jail was found to be the sixth most overcrowded prison in England and Wales.

Cardiff was also above the England and Wales average for the number of positive drug tests carried out.