Bristol prison has tightened up security on staff after metal batons went missing and have not been found.

At least one of the extendable batons used by prison officers went missing last month, sparking a complete shutdown as prisoners' cells were searched.

But after the equipment used for self defence in "extreme circumstances" did not turn up, the authorities turned their attention to the prison officers themselves.

A Prison Service spokesman told the Evening Post: "An internal investigation is under way after Prison Service equipment went missing from HMP Bristol. Procedures for checking staff who leave the establishment have been reviewed."

The spokesman would not say if, or how, procedures had now been changed due to "security risks".

According to Prison Service regulations, officers who are allowed to have batons should carry them at all times while on duty.

But the Post was given a letter by a man who was serving a brief sentence for a minor offence at the time saying at least one, possibly two, batons went missing.

The man in his 30s, who did not want to be named, said: "I was in my cell and this letter came under my door.

"It said a prison officer had lost a baton – later I heard two batons had gone missing.

"They came round and they completely stripped everyone's cell, looking for them. They also brought metal detectors round and it took about two-and-a-half days to do the whole prison.

"As far as I know they still haven't found the batons. I think it's a joke. How can you lose something like that?

"They're not flimsy little things. You never know what someone might do with them.

"I want to know why prison officers are losing batons. At the end of the day it was my first time in prison and it was an experience I never want to have again."

The "Notice to Prisoners" from the head of operations, dated February 9, stated: "An extendable baton has been reported missing. It is therefore necessary to conduct a full lockdown search.

"Until the search is completed, prisoners will be confined to their cells. There will be no association, exercise or chapel. However, visits will go ahead as normal.

"I would like to thank you in anticipation of your co-operation and patience."

The Prison Service would not confirm how many batons had gone missing. They were still to be recovered.