Flats meant for preparing inmates to be released from jail in a Grade II-listed Jacobean mansion are lying empty, a report says.
The £250,000 ex-staff quarters at HMP East Sutton Park were refurbished with the aim of housing up to 16 women ahead of their releases.
The Independent Monitoring Board (IMB) for the Kent prison said it was "a great waste of money".
A prison service spokeswoman said there was "extra capacity" at the prison.
East Sutton Park is an open prison and young offenders institution at Sutton Vallance, near Maidstone, with about 100 female inmates.
The main house is a mansion set in 84 acres of grounds and the "working prison" includes a farm, gardens and a farm shop, which is open to the public.
The flats were converted so prisoners could live "semi-independently" in preparation for returning to the community, but they remained empty months after the work was completed. the IMB said,
The board said the decision "flies in the face of the stated policy of aiding resettlement of prisoners back into society".
'Waste of money'
Peter Judges, chairman of the IMB, said: "For residents, who have served long sentences, returning to the community can be quite a culture shock.
"It is a great waste of money to refurbish the flats and then not use them, quite aside from the loss of benefit to the would-be occupants."
The prison service spokeswoman said: "The extra capacity at HMP East Sutton Park was built in anticipation of an increase in the number of female prisoners from 2018 onwards.
"Although the population has in fact decreased, this option remains open if this changes in the future."
In its report the IMB concluded the prison was "well run with residents generally enjoying a good relationship with staff".