Both firms defended their services and said they were co-operating fully with the audit.

BBC: Serco and G4S face billing probe over electronic tagging

Richard Shelby, R-Alabama, co-sponsored what they called a compromise package of safety standards for those Mexican trucks, including a safety audit for each truck firm before a U.S. operating certificate is granted, more scales and U.S. inspectors at the U.S-Mexican border crossings, and a requirement for Mexican truckers to comply with U.S. hours-of-service rules.

CNN: truck

The FSA also ordered an audit of all horse-producing abattoirs in the UK. There are five abattoirs operating that are licensed to slaughter horses in the UK and last year 8, 500 carcasses were exported to Italy, France and Belgium.

BBC: Horsemeat scandal: PM says criminals will face law