After nearly two years with Scherchen, Downes returned to England and joined the Carl Rosa Opera Company as a répétiteur. After the company's temporary closure in 1951, Downes began a long and fruitful association with the Royal Opera House, Covent Garden in 1952 with his appointment as an assistant to Rafael Kubelík. He started work as repetiteur and prompter on the same day that Joan Sutherland began with the company, his first assignment being a new Günther Rennert production of "Un ballo in maschera", shortly followed as prompter for Maria Callas in her house debut in "Norma" with Vittorio Gui conducting. His next job was singing the role of Tristan in stage rehearsals under Barbirolli, pending the arrival Ludwig Suthaus, then teaching the local singers in "Elektra".