Why are unions treated differently from other natural "corporations", i.e. churches, political parties, friendly societies, campaigning organisations, sports clubs, etc?

In 1974 the Conservative Government lost the general election and the Industrial Relations Act (IRA) 1971 was repealed by the incoming Labour Government. From 1979-97 the Conservative Government adopted a step by step approach to restructuring collective labour law. Over 18 years the Conservative Government embarked on a permanent revolution publishing 7 Green Papers, 6 White Papers, 1 Charter, revoked the 1946 House of Commons Fair Wages Resolution and the 1972 Industrial Relations Code of Practice, and enacted 9 Acts of Parliament. Statutory support for a liberty to organise ended in 1980 with the repeal of the statutory recognition procedure in the Employment Protection Act (EPA) 1975 and the passing of legislation making pre-entry and post-entry closed shops unlawful.