Conditions at the only prison in England and Wales with a unit for elderly inmates have been described as "unacceptable" in a new report.

Chief inspector Anne Owers warned that Kingston Prison in Portsmouth has "serious deficiencies" that need urgent attention.

The 126-year old prison currently holds 200 life-sentenced prisoners, including 82-year old Anthony Sawoniuk, the first man to be convicted of Nazi war crimes in Britain.

The report praised HMP Kingston as "a broadly safe and respectful prison with a good range of work and activities and an effective healthcare centre".

But it criticised the conditions in which prisoners were kept.

"Cells were effectively cubicles, divided by wooden partitions. Movement was severely restricted, there was insufficient privacy and the rooms had too little natural light, poor ventilation and in some cases no power points," said Owers.

"Staff were not trained or supported specifically to work with and motivate these elderly prisoners. Although, in theory, they were able to participate in the main prison regime, in practice we found little activity on the unit, with some elderly prisoners describing themselves as 'vegetating'."

The director general of the Prison Service, Phil Wheatley, welcomed the report.

"I am pleased that the chief inspector has recognised the excellent results being achieved at HMP Kingston in the fields of suicide prevention and substance abuse," he said.

"Her comments on the structural deficiencies of E Wing, where elderly lifers are held, are broadly in line with my own concerns about the wing, some of which are being addressed in a new building programme."

But prison reform charities warned that the report highlighted the "double punishment" suffered by elderly inmates.

"The chief inspector's report on Kingston, said to be the flagship for care of the elderly, reveals that old prisoners must suffer the double punishment of incarceration together with a standard of care which would have led to the immediate closure of any other institution for the old and infirm," said Juliet Lyon of the Prison Reform Trust.

"Whatever their age, serious and violent offenders must be detained to protect the public but they do not need to be held in such inhumane conditions with so little constructive activity."