McDonald's first British restaurant opened in Woolwich in 1974.
The Woolwich opening introduced McDonald's restaurant format and visual branding to the United Kingdom. It represented another major step in the company's international expansion after its first overseas market, Canada, opened in 1967.
McDonald's later developed a large British estate of restaurants, but the Woolwich location is the landmark associated with the chain's first entry into the UK. As in other countries, the company used its familiar name and Golden Arches while adapting menus and operations to local expectations.
The location is sometimes confused with prominent central-London sites that opened later or became more famous. Woolwich is the specific answer because the question concerns the first British McDonald's, not the chain's best-known London restaurant.