The Clumsies Make a Mess by Sorrel Anderson
HarperCollins Children's Books ISBN 9780007330904
When Howard Armitage finds talking mice in a bag under his desk, his life changes forever. And his packets of biscuits will never be the same again either! Although the mice want to help Howard get out of trouble with his evil boss, they are only good for... making a mess. This is the first book in the series about these surreal mice and their friends.