The main aim of this thesis is to examine, through an analysis of relevant case law, the way in which the courts interpret and apply primary legislation pursuant to the interpretative obligation contained in section 2(1) and (4) of the European Communities Act 1972 and section 3(1) of the Human Rights Act 1998, and to assess current judicial attitudes to the traditional concept of parliamentary sovereignty in the light of the judicial perception of the interpretative obligation in the above-mentioned provisions. As an essential prelude to the examination of the case law on the judicial treatment of the interpretative obligation in the 1972 and 1998 Acts, chapter 2 of the thesis discusses the traditional, Diceyan concept of parliamentary sovereignty. This is considered without the effects of the 1972 and 1998 Acts. This chapter demonstrates that the courts perceived it as their constitutional duty to obey and apply the latest will of Parliament without question. It is observed that no legal grounds could exist for challenging the validity or enforceability of primary legislation. Chapter 3 discusses conventional methods of statutory interpretation. It is observed that conventionally, the principal aim of statutory interpretation is the ascertainment of parliamentary intention in the statute under consideration. Where the intention of Parliament is clear and unambiguous and is not absurd in any way, the courts feel duty-bound to carry out the identified parliamentary intention in line with the rule, demanded by the doctrine of parliamentary sovereignty, that courts obey without question the latest will of Parliament. The rest of the thesis is devoted to an examination of the way in which the courts use their interpretative powers under section 2(1) and (4) of the 1972 Act and section 3(1) of the 1998 Act when interpreting and applying primary legislation coming within the purview of these enactments. It is argued that while the courts appear to continue to acknowledge the sovereignty or supremacy of Parliament, the case law reveals that in appropriate cases, section 2(1) and (4) of the 1972 Act and section 3(1) of the 1998 Act has enabled judges to interpret and apply primary legislation in a way that substantially challenges the traditional, Diceyan concept of parliamentary sovereignty. They feel able to ignore or otherwise modify the legal effects of unambiguous primary legislation in appropriate cases.