At the end of February, 708 prisoners at privately-run HMP Doncaster at Marshgate shared cells built for one according to figures revealed in parliament by the Ministry of Justice after questions from MPs.

Out of 139 prisons in England and Wales, only Wandsworth and Pentonville in London, Leeds, and Altcourse in Liverpool had more overcrowding.

HMP Doncaster, a category B jail, currently houses 1,120 men.

At Doncaster's other jails, Lindholme Prison had 120 inmates sharing single cells and Moorland Prison had 64.

Last month, it was revealed the number of prison inmates nationwide had hit a record high of 82,319 with 600 extra prisoners entering the country's jail in just three weeks - a number equivalent to a medium-sized jail.

A Ministry of Justice spokesman said the overcrowding rates were a concern.

She said: "Prisons are under pressure and we expect them to remain so over the next few months.

"We are bringing forward new measures to increase capacity and help relieve this.

" However there is nothing new in doubling up. It has been used in prisons for many years as part of efforts to maximise use of the existing prison estate."

Not all prisoners will be forced to share. Prison officers conduct a Cell Share Risk Assessment before inmates are housed together.

Those deemed to be " high risk" will not share a cell, whatever the population pressures.

The news comes as the Serco Group, Doncaster Prison's private operator announced yesterday that the company had already won various service contracts worldwide worth £1 billion this year.

This includes a £4 million contract from Doncaster Primary Care trust to provide nursing and related services at Lindholme and Moorland prisons for the next three years with options for two additional years.