Most prisoners are natives, but around one-fifth of them are non-Peruvian, and the number of UK citizens has increased in recent years. There are 32 British prisoners in Peru - three women and the rest men - the largest number in any South American country.
Peru has overtaken Colombia as the world's biggest cocaine exporter, with South American cartels supplying the lucrative European drugs market.
British cocaine smugglers imprisoned in the Peruvian jail - referred to simply as 'The Callao' - have described the terrible conditions they have endured.
ONE prisoner, who wished to remain anonymous, was told drug trafficking was an easy way to make quick money.
He said: "When I was approached to deliver drugs from South America back into the UK, I was told it would be simple, border controls were weak and I would get through easily holding a British passport. They even told me if I ate the drugs, if I took capsules inside my stomach, there would be no detection.
"On arrival at the airport, they searched my luggage and went through my bags and found nothing. Then I was X-rayed and they found me with one kilo of cocaine in my stomach."
Speaking in a film made by the Foreign Office, the prisoner and a number of other UK drug traffickers describe their shock at the conditions.
Inside Sarita Colonia, a cell built for 80 people has to accommodate about 240. Many inmates sleep in the corridors because they can't afford a bed in a cell, which reportedly cost $1000 to secure.
The prisoner said the no-one should think drug-trafficking is easy money, adding: "It never is, it never will be."
NICK was caught trying to smuggle nearly 2kg of cocaine out of Peru's international airport in Lima.
"When I decided to take drugs out of South America, I never imagined what I would face if I was arrested", he said.
Nick's illusion of making easy money came crashing down when he was arrested in April 2009.
He said: "You think that conditions are going to be the same as they are back home, until you are arrested in a developing country and you see that it is not.
"I was arrested with 1.9kg of cocaine and I still regret the day that I said 'yes' to the supplier."
Nick, from London, was sentenced to six years and eight months in prison, the standard sentence in Peru for trafficking any amount of cocaine under 10kg.
He said his experience of Peruvian prison was tougher than he ever could have imagined.
"It is really different being imprisoned abroad. You are miles away from your family, you don't speak the language", he explained.
"I mean, people joke about prison food being bad, but at least you can drink the free water.
"I'm a prisoner in a very overcrowded and very unsafe prison in South America, and there are more and more of us every day."
He added: "It's just not worth the risk."
ANOTHER inmate of Callao - in the crime-ridden port district of Lima - is deeply embarrassed for himself and his family.
The man, who did not want to be identified, said: "Last year, I was caught in South America with 12.3kg of cocaine.
"I had to call my family and explain where I am and explain what I had done. That phone call was the hardest call of my life."
Crouched on a cement slab, behind the bars of his cramped cell, the young Briton speaks of his regret.
He said: "The mistake I made not only affected me, but it also affected my family in a way that I can't imagine.
"I never thought I'd get arrested, but now I know the consequences and the effects on my life.
"My life will never be the same again. I just hope that one day I will be back with my family and start a new life, where I can be part of normal living again.
"Take my advice - don't traffic drugs."