Declan Donnelly hosts the first live semi-final of this year's contest, with the audition process having left judges Amanda Holden, David Walliams, Simon Cowell and Alesha Dixon with 40 acts to pick from. Tonight, eight of them will be performing live in the hope of impressing both the panel and the TV audience to win one of the two spots in the live grand final, where the winning act will receive a life-changing £250,000 prize and a spot at this year's Royal Variety Performance in November. (thetvdb.com)