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A trend in the late 20th century was for breweries to run their pubs directly, using managers rather than tenants. Most such breweries, such as the regional brewery Shepherd Neame in Kent and Young's and Fuller's in London, control hundreds of pubs in a particular region of the UK, while a few, such as Greene King, are spread nationally. The landlord of a tied pub may be an employee of the brewery—in which case he/she would be a manager of a managed house, or a self-employed tenant who has entered into a lease agreement with a brewery, a condition of which is the legal obligation (trade tie) only to purchase that brewery's beer. The beer selection is mainly limited to beers brewed by that particular company. The Beer Orders, passed in 1989, were aimed at getting tied houses to offer at least one alternative beer, known as a guest beer, from another brewery. This law has now been repealed but while in force it dramatically altered the industry. Some pubs still offer a regularly changing selection of guest beers.

What law required that a pub offer at least one beer from a brewery it wasn't tied to?
The Beer Orders