How Is Parliamentary Sovereignty Limited?

A significant political development in the last two decades has been the increasing presence of extra-parliamentary pressure in the form of powerful pressure groups, which has forced parliament to revise or repeal laws it has made. For example, trade unions forced the amendment of the Industrial Relations Act and the extra-parliamentary action forced the government to replace the poll tax with the council tax in the 1980's. These examples suggest that in practice, the principle of parliamentary sovereignty is limited.

Additionally, the UK has agreed, at various times, to many international agreements and treaties which place upon parliament certain obligations. For example, the UK joined NATO in 1949 and as a result, it let go of some control over defence and foreign policy. Theoretically, commitments like this do not infringe parliamentary sovereignty since parliament could decide to amend or ignore certain terms at any time, although this is not likely.