Sacred music is an integral part of the liturgy.

Two forms of sacred music are recognised as being perfectly and particularly related to the Roman liturgy: Gregorian Chant and Sacred Polyphony, though Gregorian Chant is to be given pride of place.

To fulfil this principle, there are two divisions of choirs:

The Schola Cantorum Sanctae Crucis, which is the principal choir. The Schola is to ensure that Gregorian Chant retains its pride of place in Solemn Masses on Sundays and feast days.

The Mixed Choir, the Choir of St Radegund; the Ladies Choir, the Choir of Our Lady of Ransom; and the Youth Choir. [A sample of Maternal Heart of Mary St Radegund choir singing IV Kyrie Eleison, in mp3 format.]

The place of music in the liturgy was affirmed by Pope Pius X in his Inter Sollicitudines issued Motu proprio:

Sacred music, being a complementary part of the solemn liturgy, participates in the general scope of the liturgy, which is the glory of God and the sanctification and edification of the faithful. It contributes to the decorum and the splendor of the ecclesiastical ceremonies, and since its principal office is to clothe with suitable melody the liturgical text proposed for the understanding of the faithful, its proper aim is to add greater efficacy to the text, in order that through it the faithful may be the more easily moved to devotion and better disposed for the reception of the fruits of grace belonging to the celebration of the most holy mysteries.

In light of this it is easy to understand that the fullness of the liturgy or the normative liturgy of the Church resides in the sung or solemn Mass. This was stated explicitly in De Musica Sacra, issued by the Sacred Congregation of Rites on September 3, 1958:

The more noble form of the Eucharistic celebration is the solemn Mass because in it the solemnities of ceremonies, ministers, and sacred music all combine to express the magnificence of the divine mysteries, and to impress upon the minds of the faithful the devotion with which they should contemplate them. Therefore, we must strive that the faithful have the respect due to this form of worship by properly participating in it ... It is desirable that on Sundays, and feast days the parish or principal Mass be a sung Mass.

of the PEOPLE

While the Schola and the choir are responsible for providing the sacred music for the liturgy this should not detract from the active participation of the people in singing those parts of the Mass which pertain to them. This is of great importance.

In order that the faithful may more actively participate in divine worship, let them be made once more to sing the Gregorian Chant, so far as it belongs to them to take part in it. It is most important that when the faithful assist at the sacred ceremonies, ... they should be filled with a deep sense of the beauty of the liturgy, they should sing alternately with the clergy or the choir. [Pope Pius XIs Apostolic Constitution Divini Cultus of 20 December 1928.]
At Lewisham all the laity are encouraged to sing and respond with the Schola in the various Gregorian modes in Latin at Sung and Solemn Masses.

The laity are readily familiar with the Asperges Me, the Kyrie, the Gloria, the Creed, the Sanctus, the Agnus Dei, and the Deo Gratias; as well as many Latin Hymns.