The miners' strike of 1984-85 was a defining moment in the history of British coal mining and the biggest industrial dispute in post-war Britain. It pitted thousands of miners and their trade union against then prime minister Margaret Thatcher and her Conservative government, which supported plans to shut 20 coal pits. About three quarters of the country's 187,000 miners went on strike to oppose the pit closures, which were expected to mean 20,000 job losses.