The inmates were working on the farm at HMP Prescoed near Usk, south Wales, when the 32-stone animal attacked farm manager Roger Murray.

Mr Murray - who needed 89 stitches - said he would have died if it had not have been for their swift actions.

"I'm pretty sure I was on my way out," he said. "I remember thinking :'I'm not going to make it'."

The two prisoners, Mark Collerton, 32, and Andrew Good, 33, went to his rescue within minutes.

He was bitten by the Royal Berkshire boar called Namajara, then gored by one of its tusks, and hurled into the air.

The boar left a seven-inch hole in Mr Murray's right leg - tearing through tendons and veins - but was prevented from causing further injury by the prisoners,

Both men were serving unrelated three-year sentences - Collerton for wounding and Good for theft - and both were granted their freedom 28 days early.

A prison spokesman said :"Brave actions such as these by prisoners can be justly rewarded.

"In this case, two prisoners saved the life of someone after a particularly nasty attack and their conduct merited this reward."

Paramedics were called and Mr Murray was taken to hospital.

Mr Murray's wounds were so serious he had to have extensive physiotherapy and was only able to return to work last month - nine months after the attack.

As a reward for their courage and quick-thinking, Good and Collerton were granted a Royal Prerogative of Mercy by the then Home Secretary Jack Straw.

The Royal Prerogative of Mercy dates back to the Norman conquest, but is reserved in modern times to reward prisoners for exceptionally good conduct.

There are approximately 66,000 prisoners in the UK and only about six on average are granted special remission in a year.

Another prisoner from HMP Prescoed was also granted a Royal Prerogative of Mercy recently for stopping on his way back to jail from home leave to save the life of someone injured in a motorbike accident.