It is related to, but distinct from the Gregorian chant of the Sarum use of the Roman rite which officially supplanted it by the 12th century.
The churches in Ireland and Britain had no central authority except, in theory, Rome, which in practice exerted very little influence.
As a result, Celtic chant was influenced by Spanish, Gallic, Roman, and Eastern traits.
[1] One chant typical of those that may reflect this style is Ibunt sancti, whose use was attested in Ireland.
Neither the ABA structure nor the repeated melody for the couplet are typical of the Roman chant traditions, except in Sequences, which themselves trace back to Notker of St Gall's and Tuotilo's tropes at the Irish-founded Abbey of St. Gall.