HMP Wormwood Scrubs has a “parlous” drugs problem which must be addressed immediately, says the chairman of a board looking into conditions at the prison.

Chris Hammond said more than one in five randomly selected inmates had failed drugs tests. That is nearly double the target, making the prison one of the worst rates in England and Wales.

The chairman of Wormwood Scrubs’ Independent Monitoring Board was speaking after the publication of its annual report on the prison.

Other concerns include:

The report also notes the death of an inmate last year. However, the report does point out key improvements from last year, when the IMB called the prison “dysfunctional and chaotic”, with cells painted and staff receiving better training.

But it is problems with drugs and the length of time that inmates spend in cells which concerned Mr Hammond.

He said: “21% of people that take the drug test have an illegal drug in their system. The target should be 11%. It’s one of the worst prison rates in England and Wales.

“We want minister of State for Prisons Andrew Selous to pay more money to the prison and the Met Police to have a real crackdown on drugs in Wormwood Scrubs.

“Essentially criminals are throwing packets over the walls as well as people smuggling them in. You can’t have a prison with twice the amount that is expected.”

And he said a reduction in the number of drugs detecting dogs at the prison has not helped: “The drugs dogs are now deployed on a regional basis rather then where there is acute local demand.

“We think given Wormwood Scrubs' parlous drugs state they should be at Wormwood Scrubs day after day. Sometimes go four weeks go by and the drug dogs aren’t at Wormwood Scrubs in spite of this terrible rate.”

'Government letting prisons down'

He was also alarmed at the length of time many inmates spend in their cells: “Half prisoners go off to education or work in the prison, but the other 50% are literally locked up 23 hours a day and some of these are young people aged 18-21 and others who are remanded in custody.

“The idea of prison is to rehabilitates so that when they come out they don’t reoffend. You can’t rehabilitate prisoners if you lock them up for 23 hours a day, it’s disgusting.”

However, he expects this situation to improve as the prison is in the process of getting more staff.

He also said he was “flabbergasted” to learn the prison’s x-ray machine had been broken for seven years, meaning two prison officers have to escort inmates to Hammersmith Hospital for use of the facility.

But it was not all bad news, with the IMB acknowledging an improvement. Mr Hammond said: “The new governor is getting a grip but there’s a lot of things to be done.

“There are meetings where they explain to staff what happens when someone comes in who is suicidal - all staff now know what they should do.

“And a number of cells are being painted, it’s being spruced up and internally looks better than it did last year."

Mr Hammond also called for privacy curtains in all double cells and for broken windows to be repaired.

Shadow Justice Minister and Hammersmith MP Andy Slaughter said: “The independent monitoring board’s report reveals the terrible state of David Cameron’s prisons.

“Nearly half of all prisoners in the Scrubs are confined to cells for up to 23 hours a day and over one in five prisoners are testing positive for drugs.

“In these conditions, prisons will never be able to rehabilitate prisoners or protect the public from reoffending.

“Prison staff are working hard to improve the situation but they are being let down by this Government.”

The Ministry of Justice, which runs prisons, welcomed the “significant improvements” mentioned in the report. It said new staff will recruitment will make sure all prisoners have more time out of their cells, and said it had a zero tolerance approach to “illicit material in prisons”.

A prison service spokesperson said: “We have already made it a criminal offence to throw drugs over prison walls and work closely with the police and CPS to ensure all those caught with drugs are prosecuted.

A report released earlier this year revealed the prison was, overall, one of the worst in the country.