Cecil Stephens, 46, was a 'dangerous' career criminal with a shocking record, yet he was allowed to spend most of his time outside jail earning money or enjoying himself, a court was told.
He had an £18,000 a year full-time job, made regular weekend 'conjugal visits' to see the girlfriend who later acted as his getaway driver and went on unsupervised shopping trips.
Thanks to the lax regime at the Kirklevington Grange Resettlement Prison on Teesside, Stephens was able to plan and carry out a robbery.
On the morning of the raid last December he left prison at 8am smelling of after-shave, telling guards he was looking forward to 'getting naughty' in a bed and breakfast with girlfriend Doreen Cramman, 51.
Instead she drove him 70 miles to the North Newbald Post Office in East Yorkshire and provided the balaclava and gun he needed for his raid.
Stephens was jailed indefinitely at Hull Crown Court after being convicted of attempted robbery and possessing an imitation firearm. Recorder Jeremy Hill-Baker recommended he should not be released for at least six years.
Cramman, a mother-of-three with seven grandchildren, was given a six-year jail term after being convicted of attempted robbery.
Earlier the court heard how Stephens burst into the post office shouting: 'You know the score. Just give me the money and no one will get hurt.'