SAS soldiers are believed to have been told to "save the last bullet for yourselves" if they fear they are in danger of being taken hostage by the terror group, the Express reports.
The UK's elite force were flown into the Middle East last summer, as so-called Islamic State extremists began to take control of large swathes of Iraq, adding to their territory in Syria.
Working alongside US Marines, the SAS are understood to have helped thousands of Yazidi refugees escape a massacre, as well as preventing the Islamic State takeover of the key Syrian border town of Kobani.
Reports of an order for SAS troops to "fight to the last man" rather than be taken captive by militants follows the horrifying murder of a Jordanian fighter pilot, who was burned to death by the Islamic State.
A source told the Daily Star Sunday: "The SAS have been told that if they are captured they can expect to be tortured before being beheaded, disembowelled or burned alive.
"They know there is virtually no chance of being rescued.
“Everyone taking part in the Iraq mission knows the risks.
“Most of the guys would never let themselves be taken prisoner – not by Islamic State (IS).”
Troops are also reported to have been ordered to do the "honourable thing" and call in an airstrike on any jihadist compound where they are being held.
Two incidents have seen SAS troops almost captured by the Islamic State before they were saved by US drone attacks, the newspaper added.
Yesterday, a horrifying new video released by the terror group showed captured Kurdish fighters being paraded through the street in cages.
Earlier this month, Jordanian fighter pilot Lieutenant Muath al-Kasaesbeh was shown being burned alive in a metal cage in a propaganda film released by the extremists.
He had been captured after his plane was shot down flying over Syria at Christmas.
Jordan has since stepped up airstrikes against Islamic State in response to the murder.
The Ministry of Defence do not comment on the activities of UK special forces.
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