The Monastic Office uses the Hymn composed by St. Peter Damian,

Anglorum jam Apostolus

N.B. Verses 1-5 & 6 are used for Vespers and Verses 6- 9 at Lauds.  Not all versions have the same arrangement of verses. A variant text can also be found with a verse not found in the text above.

Other Hymns for St Gregory can be found in the Analecta Hymnica,

 Summae sedis antistitis

Splendido sacra gratulans amore