Inmates claimed it was easier to get drugs than clothes or bedsheets at a prison where standards have deteriorated to "unacceptable levels", according to a watchdog report.
Inspectors found the availability of drugs, including those previously known as legal highs, was having a "serious impact" on safety at HMP Bedford.
A survey found the number of prisoners saying it was easy or very easy to get drugs had almost doubled since the last inspection of the jail in February 2014.
The number saying they had developed a drug problem while at the prison increased from 4% to 14%.
In a highly critical report setting out the findings of the latest inspection in May, Chief Inspector of Prisons Peter Clarke wrote: "The stark reality is that prisoners told us it was easier to get illegal drugs in the prison than it was to get clothes or sheets."
Drugs referred to as "legal highs" before they were made subject to a blanket ban rolled out earlier this year have been identified as a major factor in an upsurge of violence and self-harm behind bars in England and Wales.
Last week figures showed the drugs - officially known as new psychoactive substances (NPS) - have now been linked to the deaths of at least 58 prisoners.
The report from HM Inspectorate of Prisons on Bedford, which held just under 500 male prisoners at the time of the inspection, said intelligence pointed to an NPS known as Spice being prevalent. Spice mimics the effects of cannabis.
Self-harm incidents had increased "dramatically" since the previous inspection, almost doubling from 67 to 121 in the previous six months, according to the report.
HMIP also found that the physical condition of the prison was poor, with many inmates living in cramped conditions. The report detailed damaged furniture, graffiti, shortages of clothing and dirty, unscreened showers.
Of 72 recommendations made after the prison was last inspected more than two years earlier, only 12 had been achieved and four partially achieved, the watchdog found.
Mr Clarke said: "It is hard to understand how such an abject failure to address our previous clear recommendations has been allowed to happen.
"As a result, standards in the prison have declined to unacceptable levels.
"I am not suggesting that staff at HMP Bedford are not working hard - they clearly were, and some important things had been put in place to improve things in the future."
Frances Crook, chief executive of the Howard League for Penal Reform, described Bedford as "a good example of everything that is wrong with the prison system", saying: "It is unsafe, overcrowded and understaffed.
"Prisoners can obtain drugs easily but cannot get essentials such as clothes and sheets."
Justice Secretary Liz Truss has ordered mandatory testing for NPS to be introduced in jails across England and Wales.
A Prison Service spokeswoman said: "Safety in prisons is fundamental to the proper functioning of our justice system and a vital part of our reform plans.
"There are a number of factors, including the availability of psychoactive substances, that must be tackled. From today we are rolling out mandatory nationwide testing of synthetic drugs, which will help to end the flow of these dangerous drugs into our prisons.
"The Secretary of State is determined to make sure our prisons are safe and places of reform and will announce further measures this autumn."
The spokeswoman added that HMP Bedford is taking action to address the level of substance misuse.