Who specifically regulates and controls the use of antbiotics used in livestock?

The Veterinary Medicine Directorate, a Defra department, is the regulator for the use of all licensed medicines in the UK farm livestock sectors. They collate annual sales data on antibiotics and more recently have been reconciling this with antibiotic usage data submitted by the livestock sectors themselves. Their annual VARSS reports summarise progress and also detail surveillance results monitoring for the emergence of resistance genes in animals and food. The VMD in turn links into European data collected and standardised by EFSA, ESVAC and other bodies. As well as this, the VMD oversees all testing for medicine residues in food. More about their role can be found here.