Under the constitutional principles of separation of powers and Parliamentary supremacy, it is the role of the judges to interpret the law made by the executive and legislature.
Duport Steels Ltd v SIRS (1980)
.. Parliament makes the laws, the judiciary interpret them... it is for Parliament, not for the judiciary, to decide whether any changes should be made to the law as stated in the Act....
.. If Parliament says one thing but means another, it is not, under the historic principles of the common law, for the courts to correct it... We are to be governed not by Parliament's intentions but by Parliament's enactments...
Under the constitutional principle of the rule of law legal certainty is required so statute must be followed and therefore underpins interpretation and limits judicial creativity.
Spath Holme (2001)
.. Citizens, with the assistance of their advisers, are intended to be able to understand parliamentary enactments, so that they can regulate their conduct accordingly. They should be able to rely upon what they read in an Act of Parliament. This gives rise to a tension between the need for legal certainty, which is one of the fundamental elements of the rule of law, and the need to give effect to the intention of Parliament, from whatever source that (objectively assessed) intention can be gleaned....
Fothergill v Monarch Airlines Ltd 
.. it would be a confidence trick by Parliament and destructive of all legal certainty if the private citizen could not rely upon that meaning but was required to search through all that had happened before and in the course of the legislative process in order to see whether there was anything to be found from which it could be inferred that Parliament's real intention had not been accurately expressed by the actual words that Parliament had adopted to communicate it to those affected by the legislation....
Black Clawson Case 
.. We often say that we are looking for the intention of Parliament, but that is not quite accurate. We are seeking the meaning of the words which Parliament used. We are seeking not what Parliament meant but the true meaning of what they said....
The meaning of statute should be clear and explicit, but this is not always achieved. Leading to many cases concerning a dispute over the meaning of a word or phrase in a statute, which requires judges to determine the exact meaning of that particular word or phrase.
Problems with Words
Words are imperfect and can create problems through certain usage.
Words may be used to cover several possible circumstances.
London and North Eastern Railway Company v Berriman 
Mr Berriman was
maintaininga railway line, there was no lookout and he was killed. His wife tried to claim compensation.
Regulations stated the company should provide a lookout for men
relaying or repairingthe line.
The court looked at the specific words in the regulation and decided
maintainingthe line was not covered and the claim failed.
A word may have two or more meanings and it may not be clear which one should be used.
Brock v DPP (1993)
Considered confusion over the wording of the Dangerous Dogs Act 1991 and whether
breedmeant the same.
Changes in the use of language
The meaning of words can change.
Offences Against the Person Act 1861
The meaning of
grievoushas developed over the years, to have a specific meaning under the Act.
Problems with Drafting
An Act of Parliament has a long and multilayered drafting process which can contribute to issues.
The parliamentary draftsmen may have made mistakes in the original Bill which were not identified by Parliament. This can occur more often when a Bill has been heavily amended.
House of Commons Disqualification Act 1975
.. specified in Schedule 4 to this Act...are repealed.
There is no Schedule 4. However, there is a Schedule 3, which is titled
New technology may mean that an old Act of Parliament does not seem to cover present day situations.
Telegraph Act 1869
When passed the telephone had not been invented, but judges include telephones when dealing with cases under this Act.
Royal College of Nursing v DHSS (1981)
Nurses carry out abortions using procedures not known when the Abortion Act 1967 was passed.
Legislation can fail to address specific circumstances.
Twining v Myers (1982)
The court had to decide whether
roller skatesamounted to a
Words not used
Certain words may be regarded as being implied so not used.
Role of Interpretation
As there is potential for uncertainty it is inevitable that issues must be resolved by judicial interpretation. Techniques and guidelines have been developed to assist judges in this process, the rules of statutory interpretation. These have evolved through the common law and are judge made. However, Parliamentary Sovereignty is maintained because if Parliament does not like the definition produced by a court, it can choose to amend the statute to make meaning explicit or pass new legislation which overturns the court's decision.