UK citizens visiting Spain for tourism or business purposes for less than 90 days do not require a visa, but must have a valid passport. The passport must be valid for at least 6 months beyond the intended date of departure from Spain.
UK citizens who wish to stay in Spain for longer than 90 days, work in Spain, or establish a business in Spain, must apply for a visa.
It is important to note that these requirements are subject to change. For the most up-to-date information, please consult the UK government's travel advice website or the Spanish embassy or consulate website.