Not my words, but the result of a little research.

It will be seen that a ministerial statement IN PARLIAMENT may under the rule in Pepper -v- Hart assist in the construction of a statute that is otherwise ambiguous or of unclear meaning in context. Asserting that a minster's assurance in correspondence governs otheriwse clear statutory words? Put it this way, don't expect me to do it on a contingency basis!

Long quote follows: -

EXTRINSIC AIDS
Royal/Law Commission reports and White Papers
These have been admissible since the case of Davis v. Johnson [1978] AC 264, which said that "the report may be used to identify the mischief the legislation is intended to remedy but not to construe the enacting words") and other travaux préparatoires providing (Fothergill v. Monarch Airlines Ltd. [1980] 3 WLR 209) that it is material in the public domain clearly intended to be the first stage in the legislative process and, if the document is a treaty, that a literal construction is in conflict with the purpose of the treaty, or if the legislation is ambiguous.

However, documents released under the 30 year rule may not be used (JH Rayner v. DTI 1987, affirmed by Pepper v. Hart), since it is unreasonable to allow secret documents to be used in court.

Hansard
Hansard has been officially used (judges used it before this case unofficially) since the case of Pepper v. Hart, in which the question was whether the taxable benefit of providing the children of teachers with free education should be taxed at the nominal extra cost to the school, or at the normal cost of the school's fees. It was decided using Hansard that it should be taxed at the lower cost.

In this case it was said that if Hansard "clearly discloses the mischief aimed at or the legislative intention lying behind the ambiguous or obscure words", then it is an admissible aid to construction.

However, it was said that "I cannot foresee any statement other than the statement of the minister or other promoter of the Bill is likely to meet the criteria".

In addition it was said that "if a minister clearly states the effect of a provision and there is no subsequent relevant amendment to the Bill or withdrawal of the statement it is reasonable to assume that Parliament passed the Bill on the basis the provision would have the stated effect".

Pepper v. Hart means that the will of Parliament will more frequently be followed, thus reinforcing parliamentary supremacy.

However, it the inevitable result is increased costs as more research is conducted into Hansard and other sources.

Hansard is, of course, not binding on the courts - there is no reason why they should not ignore the intent of Parliament unless it is expressed in a statute. Hansard has the same legal status as any other interpretative aid.

The question arises whether Pepper v. Hart affects stare decisis, that is to say whether a court can overrule an otherwise binding case on the basis of Hansard showing that the previous construction was wrong. If this question were to be answered in the affirmative, magistrates courts could overrule the House of Lords.

Common sense might suggest that incorrect interpretations should be overruled, but there is the issue of separation of powers - according to the traditional doctrine of the separation of powers the judiciary must be free to reject the Hansard material, since it is nothing more than an interpretative aid, which were it to be binding, would make Parliament both legislator and interpretor: legislation has traditionally been seen as an abstract document not tailored to particular situtations, but rather being a list of abstract principles interpreted and applied in individual cases by the judiciary. Taken this way, to give Hansard such as status would apparently contravene HA Hayek's conception of the rule of law.

On the other hand it seems rather futile for Parliament to make laws if the courts are not going to enforce them according to its intention.

Other aids
Dictionary definitions - this implies a literalist construction of statutes, since a purposive approach would seek to enforce what Parliament intended, rather than enforce the meaning of what it said.
Legal textbooks
Treaties (e.g. EU treaties), where the law was intended to enact the treaty
EU directives