This article explains the large mario and sonic numbers in the UK
http://www.gamasutra.com/php-bin/news_index.php?story=16579
The game’s sudden rise to the top can be attributed in large part to its inclusion in several unofficial retail hardware bundles – generally the only way the supply constrained Wii is now sold in the UK. Similar bundles also accounted for the sudden re-appearance of Mario Party 8 at number four in the charts, as well as Rayman Raving Rabbids 2 at number twenty.