NCB in managing the industry and discouraged strikes. Under the chairmanship of Alf Robens, pit closures became widespread as coal's place in energy generation declined. The NUM leadership continued to resist calls for strike action, but an unofficial strike began in 1969 after a conference pledge on the hours of surface-workers was not acted upon. This was a watershed moment that led to increased spending on the coal industry and a much slower rate of pit closures, as well as the election of more militant officials to the NUM leadership. Under the government of Ted Heath, an official strike in 1972 won increased wages after the Wilberforce Commission. Less than two years later, Heath called a general election over another official strike, called after an overtime ban had led to a Three Day Week in Britain, and lost the election to the Labour Party. The wage demands were then met and spending on the industry continued to increase, including the establishment of the new Selby Coalfield. By the early 1980s, many pits were almost 100 years old and were considered uneconomic to work at current wage rates compared to cheap North Sea oil and gas, and in comparison to subsidy levels in Europe. The Miners' Strike of 1984 failed to stop the Conservative government's plans under Margaret Thatcher to shrink the industry, and a break-away Union of Democratic Mineworkers was founded by miners, mostly in the Midlands, who felt that the NUM had broken its own democratic rules in calling the strike. The National Coal Board (by then British Coal), was privatised by selling off a large number of pits to private concerns through the mid-1990s. Because of exhausted seams, high prices and cheap imports, the mining industry disappeared almost completely, despite the militant protests of some miners. In January 2008, the South Wales Valleys last deep pit mine, Tower Colliery in Hirwaun, Rhondda Cynon Taff closed with the loss of 120 jobs. The coal was exhausted. Until 2015 coal was still mined at Hatfield, Kellingley and Thoresby Collieries, and is extracted at several very large opencast pits in South Wales, Scotland and elsewhere. Kellingley Colliery was the last deep coal mine in operation in the UK and its last coaling shift was on 18 December 2015 when coaling operations ceased with the loss of 450 jobs bringing deep coal mining in the UK to an end in its entirety,