Shocked father Stephen Forse spotted the mouse in a loaf he was using to make sandwiches for his children.Mr Forse bought the bread from Tesco Online and had already used some of it when he noticed "a dark-coloured object embedded in the corner of three or four slices".
The 41-year-old father from Kidlington in Oxfordshire first though it was a section of unmixed dough but quickly realised his mistake.
"As I looked closer, I saw that the object had fur on it," he said.
The situation was made even worse when an environmental health officer, who had called to gather evidence, found that the mouse was without a tail.
"Her comments made me feel ill once again as there was no indication as to where the tail was," said Mr Forse.
"Had it fallen off prior to the bread being wrapped or had any of my family eaten it with another slice of bread on a previous day?"
Manufacturer Premier Foods was fined £5,500 and ordered to pay £11,109.47 in costs at Oxford Crown Court for failing to maintain acceptable standards at their site in Mitcham, south London.
A spokesman for Premier Foods said: "We apologise profusely for the distress caused as a result of this isolated incident."