A report from the Prison Reform Trust, launched at HMP Brixton, comes the day before prisons minister Andrew Selous is due to give evidence on older prisoners to the Justice Select Committee.
People aged 60 and over and those aged 50 to 59 are the first and second fastest-growing age groups in the prison population, the report said. Between 2002 and 2014, there was an increase of 146 per cent and 122 per cent in the number of prisoners held in those age groups respectively.
As at March 31 there were 102 people in prison aged 80 and over and five people in prison who were 90 or older.
Juliet Lyon, director of the Prison Reform Trust, said: “Despite a Ministry of Justice commitment to transform rehabilitation, in the last few years, prison has been reduced to a punitive holding operation for people growing older and sicker behind bars.
“Crisis management, drastic budget cuts, shedding and now desperately trying to recruit staff have all distracted prison managers from planning properly for a changing prison population.
“Overall, prisons are less safe and less decent than they were even a year ago when we published our last report. An incoming administration of government in May 2015 must not accept this deterioration in prison standards and conditions as the new normal.”
Longer sentences mean people in prison are growing old and frail with high rates of unmet social care and support needs, according to the PRT.
Two in five of those over the age of 50 in prison have a disability, the report added.
Earlier this year, one prisoner wrote to the Prison Reform Trust: “I am 65 years old and work full time.
“Really I am one of the lucky ones. Some of the prisoners are disabled 70, 80 years old, locked behind their doors, no TVs, some have no radio, banged up 5.30 evening until 10, 11am next day with no hot water, not opening for hot water for a drink.
“Not opening for them to go for medication, resulting in one man being taken to hospital. Another has self harmed.”
The facts and figures highlight the changing face of the prison population, which has risen by a fifth in the past 12 years and now stands at around 84,500 in England and Wales.
Elsewhere, the report shows that overcrowding and resource pressures have pushed prison managers into mixing people held on remand with sentenced prisoners.
Prison managers are also increasingly mixing young people aged 18 to 20 with adult sentenced prisoners.
Over the past three years, the National Offender Management Service has had to deliver £749 million savings and is expected to make a further £149 million cuts in 2014/2015.
Between March 31 2010 and June 30 2014 the number of Full Time Equivalent staff employed in the public prison estate fell by 28 per cent, a reduction of 12,530 staff.
Last year a report by the Justice Select Committee said prisons in the UK are struggling to cope with a rapid growth in the number of older inmates, partly caused by an increase in convictions for historic sexual offences.