And the overall price of converting Wealstun prison near Wetherby into a secure jail is £23m, the YEP can reveal.

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The government announced two years ago that the open prison was to become fully closed with greatly-increased capacity and new secure fencing.

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In recent years the prison, which often houses long-term inmates shortly before release, has been at the centre of several "escape" incidents.

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One man was found working in a nearby pub and another set up a gardening business in the area.

A new gate house, a visitor reception, car park, dining hall and kitchen, workshops, gym and education rooms at the jail have cost £18.5m.

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Converting to a secure jail has required new cells to be built at a cost of £178,000 per prison place.

Labour says the high cost is evidence of why the Conservatives are wrong to suggest converting more open jails. Justice Secretary Jack Straw said: "These plans will be very expensive and fraught with difficulties. I hope the Conservative Party have talked to local communities about them before making this announcement."

Wealstun was created in 1995 out of a merger of Thorp Arch and Rudgate and was previously partly open and partly closed. It offered trade training , with prisoners working in the local community.

The open prison closed last year for its conversion and is now operating as a category C closed prison.

A Prison Service spokesman said: "The work on Wealstun is now complete. We will always ensure there is sufficient capacity to hold those who should be behind bars, to protect the public and continue to make communities safer.

"The Government remains committed to providing additional capacity and modernising the prison estate.

"We have created 25,000 additional prison places in the last 12 years and are pursuing an extensive building programme to increase net capacity to 96,000 by 2014."

The Tories recently dropped plans to sell Leeds and Wetherby prisons to private developers and replace them with newly-built jails elsewhere in the region.

Their plans to sell up to 30 jails and use the proceeds to fund 5,000 new prison places have been undermined by the collapse in the property market.

Conservative officials say that they have drawn up a "back up plan" to convert some former army barracks into jails and turn some open prisons into closed Category C jails.

However, Labour say there are "significant practical difficulties" in converting the country's 17 remaining open prisons, including one open prison which has an eight-mile perimeter.