In 1979, Margaret Thatcher became Prime Minister of the United Kingdom. Her policies of free market economics soon clashed with the loss-making, government-owned National Coal Board. In 1984 and 1985, after the government announced plans to close many mines across the UK, mineworkers went on strike. This strike, and its ultimate failure, led to the virtual destruction of the UK's coal industry over the next decade, although arguably costs of extraction and geological difficulties would have had the same result, perhaps a little later. No deep coal mines are left in the valleys since the closure in 2008 of Tower Colliery in the Cynon Valley. Tower had been bought by the workers in 1994, despite government attempts to close it.