The 39-year-old X Factor judge was hosting the show, alongside Sarah-Jane Crawford, but was running late and was spotted rushing up the red carpet with husband Stephen Belafonte.
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Speaking to The Sun, a source said: "Mel looked really flustered. She'd gone to a place she thought was safe to smoke but security demanded she go outside until she'd finished. She wasn't getting any special treatment.
"It was real drama as she was the host and it was live on ITV2, so she couldn't risk not being there."
After a rehearsal allegedly ran over, which was what caused her to be late, another source claimed Mel was complaining to Stephen about the amount of people she had to walk through to get inside.
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But the former Spice Girls singer's rep denied the smoking claims, telling the Mirror: "This story is false. Mel did not light up a cigarette in the backstage area. The show rehearsals ran late meaning less time on the red carpet."
Luckily for Mel, the rest of the show went much more smoothly and saw her include a whopping seven outfit changes.
Posting a picture of the first to Instagram, Mel wrote: "The 1st of 7 of the @Julienmacdonald dresses for the #MoboAwards2014 and yes I am wearing underwear"
Mel was accompanied to the show by Stephen and her eldest daughter Phoenix Chi.