The United Kingdom has several types of visa, some of which allow the holder to work in the UK. 

The UK is a member of the European Union, and all residents of EU member countries are eligible to work within the UK without a visa. Individuals who are married to EU citizens also have that right, provided they are coming to the UK with their spouses. Beginning in June 2002, citizens of Switzerland no longer need a work permit or visa to work in the UK.

Residents of Australia, New Zealand, South Africa, Canada, and Malaysia are eligible to obtain an ancestry or spousal visa for the UK if they have a grandparent or parent who holds a UK passport. This allows them temporary residency in the UK for a period of four years, during which time they are permitted to work on a temporary or permanent basis. The spouse of someone who has an ancestry visa is also eligible to apply for this type of visa.

This is just a sample of what you'll find in the complete UK guide.