The Citation read:
For most conspicuous bravery and initiative during the operation near Cambrai 27 September to 1 October 1918.
On 28 September, when the advance of the Brigade was held up by fire from both flanks and by thick, uncut wire, he crawled forward alone and explored the wire until he found a small gap through which he subsequently led his men and forced an entry into the enemy trench. The enemy counter-attacked in force, and, through lack of bombs, the situation became critical. Although wounded, Lieutenant Gregg returned under terrific fire and collected a further supply. Then, rejoining his party, which by this time was much reduced in numbers, and in spite of a second wound, he re-organised and led them with the greatest determination against enemy trenches, which he finally cleared. He personally killed or wounded 11 of the enemy and took 25 prisoners, in addition to 12 machine guns captured in this trench. Remaining with his company in spite of wounds, he again on 30 September, led his men in attack until severely wounded.
The outstanding valor of this officer saved many casualties and enabled the advance to continue.
For this valor he was awarded the Victoria Cross.