Sanitary bins are a legal requirement in the workplace in the UK. Every business in the UK is legally required to provide appropriate facilities and means for the disposal and collection of sanitary products in female washrooms. This is covered in The Workplace (Health, Safety and Welfare) Regulations 1992, the Water Industries Act 1991, and the Environmental Protection Act 1990.
Failure to provide adequate sanitary bins in your workplace bathrooms could be a breach of these legal regulations and result in a large fine. Having sanitary waste bins present in workplace washrooms helps keeps staff and visitors comfortable, so should be a priority a an employer anyway.