Lewis won the most public votes in what judge Simon Cowell said was the toughest semi-final so far, while Asanda won the judges' vote for second place by three votes to one, after she and Alex Keirl completed the top three in the public vote.
Lewis had the judges roaring with laughter with her impressions and judge Amanda Holden anticipated the verdict of the viewers when she told the married mother of two from Hertfordshire: "You were the best act of the night."
Cowell told her: "It's really hard to be up there without any music, any props."
Asanda performed Halo by Beyonce and was told by judge David Walliams: "You really owned that song."
The controversy over having children on the show which has rumbled on all week following criticism from Sir Bruce Forsyth reared its head again briefly as Cowell told Asanda: "OMG. Seriously, forget how old you are, and there has been a lot of debate over this, but it just doesn't matter, if you've got it, you've got it, right."
Cowell has been caught up in a war of words with Sir Bruce after the showbiz veteran said youngsters faced "emotional damage" from the pressure of performing.
Those missing out included highly praised ballroom dancers AJ and Chloe, magician James More, whose act was called "fabulous" by Cowell, and Keirl, 20, who performed The First Time Ever I Saw Your Face, by Roberta Flack, and was told by Holden: "You've got a beautiful gorgeous voice."
Which of this lot do you think is the best of the British Talent on display this year?