In the past two years, nearly 350 people have been caught posting entries on Facebook while serving a sentence, Ministry of Justice figures show. All the profiles were closed by Facebook following investigations by prison officials. 

It is likely that hundreds more have successfully used the site without authorities being made aware.

Inmates are banned from using the internet but access the web through mobile phones smuggled into jails.

The revelation drew criticism from campaigners yesterday. Javed Khan, of Victim Support, said: "Offenders using Facebook from prison makes a mockery of the idea that they are being punished."

Jean Taylor, from Families fighting for Justice said: " These perpetrators should not be able to have access to mobile phones in prison.

"They are getting away with torturing their victims. The social networking sites should police this much more closely!"

Two years ago it emerged that Colin Gunn, one of Britain's most dangerous gangsters was using Facebook to threaten his enemies from a high security prison cell.

In one posting Gunn wrote: "I will be home one day and I can't wait to look into certain people's eyes and see the fear of me being there.

"It's good to have an outlet to let you know how I am, some of you will be in for a good slagging and some have let me down badly and will be named and shamed ***ing rats."

The 44-year-old was jailed in 2006 for the revenge killings of John and Joan Stirland.

Recently a teenager who killed a shopkeeper posted a series of pictures on Facebook showing him making gangster salutes.

A Facebook spokesman said: "If something is happening which violates our use policy we will be very active and robust in removing it."