Prisoners released by mistake, figures show
Sixty-nine prisoners were freed from British jails by mistake last year, figures obtained by the BBC have shown.
The statistics for 2009 to 2010 were disclosed after a Freedom of Information Act request.
Among those wrongly released were sex offenders, burglars and people convicted of violence and robbery in England, Wales and Scotland.
The Prison Service said such mistakes were "rare but regrettable".
BBC home affairs correspondent Danny Shaw said although the government has provided some information before about prisoners released in error, this was the most comprehensive set of figures yet.
They showed 63 inmates were wrongly freed from jails in England and Wales last year, and six from Scottish prisons. The total more than doubled in two years.
The figures also revealed that since 2007, 39 prisoners serving sentences for violence, assault or robbery were freed by mistake, as well as six sex offenders.
The vast majority of prisoners inadvertently let out were sent back to jail but five are understood to still be at large.
It is thought most mistakes were due to prison staff miscalculating release dates because of complex sentencing arrangements.
A spokesman for the Prison Service of England and Wales said most prisoners released in error were returned to custody quickly.
"The number of releases in error remains very small as a percentage of total discharges. This type of error is a rare but regrettable occurrence," he said.
He added that the Prison Service has developed robust procedures to deal with such situations and said the service took public protection extremely seriously.