Dermot O'Leary hosts the star-studded version of the singing contest, in which the line-up of famous faces leave their comfort zones and take to the stage to perform - and while some have proved to be naturals, others have struggled somewhat. Simon Cowell mentors the Groups, Nicole Scherzinger is in charge of the Overs, and Louis Walsh handles the Unders, and as usual the judges are each allowed to send one act through to next week by pushing the golden buzzer, leaving the rest at the mercy of the voting public.