Portland's Verne prison will have a new role when it reopens this year – as a jail exclusively for sex offenders.

It will be one of a handful of UK prisons dedicated to holding sex criminals in response to an increase in the number of abusers.

It is the latest role for the institution, a former Victorian military barracks, which was a jail for 60 years before turned into an immigration removal centre (IRC) for the Home Office.

After almost four years, the IRC closed in January as it was announced it would return to its role as a men's Category C prison.

It is understood a substantial amount of money has been invested in converting it back to a prison to ensure it is safe, secure and fit for purpose.

The Prison Service said it did not have a final figure for the cost of conversion.

A spokesman said it is expected to house 580 offenders – a similar amount to when it was a prison previously.

Staffing levels will be confirmed in due course.

It is understood among its facilities for inmates will be a sex offender treatment programme.

A Prison Service spokesman said: “The Verne will become a closed prison for category C men convicted of sexual offences later this year.

“Protecting the public is our priority and, as with all closed prisons, it will have strict security measures.”

It has been previously stated by the Ministry of Justice that evidence shows that holding sex offenders together makes them more likely to engage in treatment programmes. It is also better value to taxpayers as resources are targeted where they are most needed.

A Prison Officers' Association spokesman welcomed the fact the Verne would reopen again, creating jobs and benefitting the local economy.

He said it would be an opportunity for employees, who had been displaced when the prison or IRC closed, to return to the island as they would have been on detached duties elsewhere.

The spokesman added there may be additional pressures on the emergency services when the prison reopens.

South Dorset MP Richard Drax said: "The fact is we have two prisons employing large numbers of people and they are continuing and that is extremely good news.

"With the prison estate being reviewed it's always a concern with older prisons being seen as vulnerable but I'm very glad to see both Portland prison and the Verne continue. As well as employing prison staff there are other spin-offs for the local economy."

Regarding the type of prisoner that will be held there, Mr Drax said: "A prisoner is a prisoner.

"They're not going to get out, they won't pose a threat to the local community."