Nick Levine of Digital Spy gave the song a positive review stating:
We Brits have been surprisingly sniffy when it comes to homegrown pop-punk girlies - just ask everyone from Love Bites to Alex Roots - but 16-year-old Daisy Coburn could be the one to eradicate the collective sneer. She's blonde and photogenic, blessed with plenty of 'tude and has even bagged a Chipmunk cameo for her debut single. Well, what are labelmates there for, eh?
Best of all, the single itself is a bit of a blast. Inspired by adolescent squabbles with Daisy's "really neurotic" sister, 'Number One Enemy' is a synthy little pop-punk ditty with nearly as much fizz as a Mento dropped in a bottle of Coke (if you haven't tried it, do). "Take off, take off, Daisy's about to take off," Chipmunk predicts around two-thirds through. When the big catchy chorus hits, you won't find it hard to agree.
A music video is available for the song. The video features Daisy dancing around a colourfully decorated garden, and later features her dancing around a decorated stairwell. During his verse, Chipmunk is seen sat at a long wooden table, in which Daisy is stood dancing behind him. Various odd objects appear throughout the video, although notable a giant cupcake and rainbow coloured sheep. The video seems to be inspired in parts by Lewis Carroll's Alice's Adventures in Wonderland and Through the Looking-Glass and What Alice Found There, as seen by Daisy holding a pig, the long table (reminiscent of the tea party table) and Chipmunk holding a hat similar to the Mad Hatter's. We also see Daisy encountering a white rabbit and following it down a rabbit hole at the start, a small bottle reading "Drink Me", signs saying "This Way" and "That Way", a small house (reminiscent of when Alice grows larger whilst inside the White Rabbit's house) and oversized or just plain out-of-the-ordinary objects and surroundings.
Following its release on 1 March 2010, "Number One Enemy" debuted in the UK Singles Chart on 7 March 2010, where it peaked at #13. The following week, the single fell 6 places to #19. On 21 March 2010, the single fell a further 8 places to #27 and the following week fell a further 7 places to #34, meaning the single has spent 4 weeks in the UK Top 40 to date. After 5 weeks in the UK Top 40 Number One Enemy dropped out of the chart. on 20 March 2010, "Number One Enemy" debuted in the European Hot 100 Singles where it peaked at #40