From 1913 until 1984 to use their resources for political purposes, unions were lawfully required to ballot members to establish political objects as part of their rules and to maintain separate political funds in order to do this. Only unions with political funds could use these to support political parties.
In 1984, this legislation was extended by the Conservative government to require decadal review ballots on maintaining these funds and the definition of political activity was changed so that this potentially restricted the ability of unions without political funds to campaign on issues affecting them which were the result of government policy.