More than half of prisons in England and Wales are overcrowded, according to figures obtained by the Prison Reform Trust.

The campaign group warns more than 10,000 people are held in the prison system than there is capacity for, with 15 jails full beyond even their safe overcrowding limit.

And in a report published this weekend, the trust says conditions are getting worse, with more than 17,000 prisoners now held two to a cell built for one.

It notes the 26 self-inflicted deaths in custody since the beginning of June, of which 24 have taken place in overcrowded prisons, and warns the problem warrants urgent attention.

New Home Office figures, she claimed, suggest the prison population could go as high as 90,000 by the end of the decade.

"Prisons may exceed their certified normal accommodation, the figure at which the prison operates comfortably, but we do not operate above the operational capacity," a Home Office spokeswoman said.

"On some occasions prisons are listed as having populations higher than their operational capacity.

"The reason is most often attributed to the fact [that] a prisoner or a number of prisoners are absent on authorised absences, such as when a prisoner is recorded as part of an establishment's population but is held outside, for example in hospital or on release on temporary licence."