Figures from Nielsen BookScan, which measured book sales between 9 November and 12 November, put the Mog book at the top of both the children’s and adult’s best-seller charts.
The book is only on sale at Sainsbury’s and costs £3, with a minimum donation of £2 from every book going to Save The Children’s literacy programme.
According to the Nielsen figures, Sainsbury’s has sold an average of 39 copies of the book per minute between 13 November and 17 November.
Ann-Janine Murtagh, the executive publisher of HarperCollins Children’s Books, which published the book, said: "It’s fantastic to see Mog's Christmas Calamity take the number one spot as the biggest selling book in the UK."
"It is a testament to the magic of Judith Kerr's storytelling and the enchanting film that has been produced. Most significantly each book purchased is raising funds to help more children in the UK delight in the pleasure that reading can bring – I think Mog would be proud."
Abbott Mead Vickers BBDO was the agency behind the "Mog's Christmas Calamity" campaign, which also included a three-and-a-half minute TV spot, bringing the Mog story to life through a mixture of live action and animation. The ad has been viewed nearly 12.5 million times on YouTube.
Sainsbury’s is also selling a Mog stuffed toy, which a source told Campaign was close to being sold out.
AnalogFolk has created an accompanying digital campaign encouraging people to upload videos to social media that show them reading the Mog story to a child. The footage will be used to create a montage that tells the story of Mog's Christmas Calamity from beginning to end.