The UK has stringent requirements for the welfare standards of animals used in science. The requirements are set out in the Guidance on the operation of the Animals (Scientific Procedures) Act 1986 (ASPA) that explains how the act is administered and enforced https://www.gov.uk/guidance/guidance-on-the-operation-of-the-animals-scientific-procedures-act-1986
All establishments that use animals in science must fully comply with the Code of Practice for the housing and care of animals bred, supplied or used for scientific purposes. The Code provides advice about the way in which those responsible under ASPA may comply with those requirements. https://www.gov.uk/guidance/animal-research-technical-advice#code-of-practice-for-the-care-and-accommodation-of-animals
All licensed establishments are inspected by the Home Office Animals in Science Regulation Unit to provide assurance of compliance with the requirements of ASPA. All Home Office inspectors are fully registered medical practitioners in the UK or Members of the Royal College of Veterinary Surgeons.