I hoe that Mr. England will not be offended if I graciously suggest he is, in fact, a little early liturgically, Veni Emmanuel being based on the Great 'O' Antiphons, which properly belong to Vespers of the latter days of Advent, starting on 17th. December with O Sapientia.
This does, of course, give me chance to post on a couple of chants proper to the whole of Advent. First, the office hymn for Vespers, Creator Alme Siderum - here is a nice version by the choir of the Carmelite Priory, London:-
It is possible that you might also come across the more archaic version of this hymn, Conditor Alme Siderum , which is preserved in some usages, notably the offices of the Dominican Order. Here is a version from Blackfriars Oxford:-
The hymn is followed by the opening versicle of Rorate, Caeli ; here is the full version:-
Ye Heavens, drop down from above, and let the the clouds rain down the Just One!