Criminals have won more than £1 million in taxpayer-funded compensation over delays in parole proceedings, a new report reveals.
Offenders whose cases are held up can claim payouts under human rights laws - even if they are ultimately kept behind bars.
The Parole Board for England and Wales paid £1.1 million in compensation claims to prisoners from April 2011 to March last year as a result of delayed hearings, an official spending watchdog disclosed.
More than half a million - £554,000 - was paid out in 2015-16 - more than six times the annual sum recorded three years earlier.
The National Audit Office (NAO) said delays mean some prisoners may have spent longer in jail than they would have if their parole hearing had been held sooner.
Those who experience hold-ups can claim compensation under the Human Rights Act once their case is concluded.
Convicts can claim at a rate of around £50 per month of delay if they are turned down for parole. If they are released following a delay, they can claim at a rate of around £650 per month.
The board received 463 private law damages claims in 2015-16, compared to 89 in 2014-15.
The NAO report said: "As the board attempts to reduce the backlog of outstanding cases, it will crystallise its liability for an increased number of potential compensation claims, and compensation costs may increase."
The board is responsible for deciding whether prisoners can be safely released from prison, and advising on movement between closed and open prisons across England and Wales.
There was an "immediate impact" on the demand for oral hearings conducted by the body in the wake of a legal ruling in October 2013, the NAO investigation found.
While the overall number of cases received has remained stable in recent years, oral hearings soared to a high of 7,148 in 2015-16.
The number of outstanding cases increased by more than 140% following the ruling, reaching a peak of 3,163 in January 2015, according to the report.
It found the board's ability to reduce the backlog is limited by the number of cases that can be listed per month.
And once scheduled, hundreds of hearings are deferred or adjourned, often because reports are unavailable or incomplete.
As well as growing costs relating to compensation payments, the board has seen spending on members' fees rise due to an increased oral hearing workload.
Members do not receive salaries but are paid fees based on the work they do on a part-time basis.
While the number of members has been falling, spending on their fees has increased from £4.7 million in 2010-11 to £6.7 million in 2015-16.
In 2015-16, 16 members earned more than £70,000 and three earned more than £100,000, the report said.
Professor Nick Hardwick, chair of the Parole Board, said: "I am pleased the NAO has recognised the huge challenges the Parole Board faced as it dealt with more cases and more oral hearings with fewer Parole Board members.
"As a result, the backlog of outstanding cases grew, with unacceptable delays for victims and prisoners. Given the scale of the challenge it has taken time to put things right.
"I am pleased the NAO recognises the progress we have made. We have a new strategy, have recruited over 100 new members and our backlogs are down by over a third."