 After interpreting the role of Rinaldo in Antonio Sacchini's "Armida", which was given at Milan's "Teatro Regio Ducale" during the 1772 Carnival season, Millico decided to partner the composer in his moving to London, in order to serve as the ""primo musico"" (principal castrato) at the King's Theatre.Here he performed the leading male roles in the first London operas by Sacchini ("Il Cid" and "Tamerlano", both in 1773).He was also involved in a failed attempt to counteract "the progressive watering-down, pasticcio-fashion," of Gluck’s "Orfeo" which had been initiated in London in 1770 with the active participation of Guadagni.