The 49-year-old presenter told how BBC bosses decided to remove all references to fire, just over two weeks on from the inferno in West London which left many residents dead and unaccounted for.
Tonight’s six groups included an a cappella group from King's College London All The King’s Men, a Polish jazz group Alle Choir, the London International Gospel Choir, a female vocal soul group Songbird Sessions, a Welsh choir Sgarmes and the newly formed 4 Tune Tellers and Kimmy.
Introducing the head-to-head battle round, Mel said: "One group is about to be knocked out of the competition.
"The other will face All The King’s Men in tonight's solo battles. Deciding their fate is the ever dramatic Riff-Off."
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Police officers arrive at Dorney Tower residential block on the Chalcots Estate in north