Most prime ministers in parliamentary systems are not appointed for a specific term in office and in effect may remain in power through a number of elections and parliaments. For example, Margaret Thatcher was only ever appointed prime minister on one occasion, in <answer>1979</answer>. She remained continuously in power until 1990, though she used the assembly of each House of Commons after a general election to reshuffle her cabinet.
When was Thatcher appointed prime minister?
1979