A security alert was launched at a prison after a gun was found in a cell during a raid.

Officers at Lewes Prison stormed two cells and uncovered an imitation gun made from a cigarette lighter case and matches.

The officers launched |the search following a tip-off that an inmate might be plotting to use the gun to threaten staff in a breakout attempt.

The incident happened on February 21 but it has only now come to light after a restricted bulletin sent to prison staff was leaked to a national newspaper.

The memo described the weapon had the “capacity to threaten or coerce” and was believed to have taken months to construct.

However, Neil Ambrose from the prison’s independent monitoring board said he did not believe the incident was treated as a security risk but as an “act of stupidity” on behalf of the prisoner.

He added that he believed the prisoner only received a ticking off for the incident and not any formal punishment.

Dr Ambrose said: “I don’t believe it was seen as a credible weapon that could have been used in an escape attempt.

“I think the prisoner was probably told off and told not to do it again.

“He would have been charged for owning an item he was not allowed rather than with a firearms offence which obviously is much more serious.

“In most cases, prisoner weapons are usually makeshift blades used to resolve prisoner on prisoner conflicts, not common for |them to be used in escape attempts.

“Prisoner made weapons is not a particular problem at Lewes because it gets most of its inmates from the courts in Sussex – it doesn’t have the gang problems like you would see in a London prison.”

He added that it was likely there could be a Ministry of Justice investigation into how the details of the incident were leaked to the press.

He said the monthly security bulletins are restricted and not publicised in case they assist other prisoners.

A Prison Service spokesman said: "This find demonstrates the vigilance of staff at HMP Lewes and shows that our rigorous security measures are working.

“We take the safety and security of staff and prisoners very seriously and cells are checked every day.

“The perpetrator of this offence was punished appropriately by the prison.”