Imperial Tobacco v Lord Advocate  UKSC 61; 2013 SC (UKSC) 153
 Much of the discussion in the Court of Session was devoted to the question whether a different approach should be taken to the interpretation of the 1998 Act from that applicable to other statutes because it was said to be a constitutional instrument. I do not think that it is necessary to dwell on that issue at length at this stage. The Dean of Faculty accepted that the object was to arrive at the true meaning of the statute. Its content might influence the approach to be taken, but assertions about its constitutional nature were not in point. He acknowledged that the exercise to be undertaken was in essence no different from that which was applicable in the case of any other UK statute.
 Senior counsel for the Lord Advocate and the Advocate General were, however, not entirely at one as to the approach that should be adopted. For the Lord Advocate it was stressed that a construction should be avoided which would render the endowment of plenary law-making powers on the Scottish Parliament futile. The Advocate General, for his part, said that it would be wrong to favour an expansive approach to the meaning and application of the provisions about legislative competence. Asserting that the purpose of the 1998 Act was to devolve plenary legislative power on the Parliament did not assist in determining the actual scope of what it was designed to achieve. The Dean of Faculty said that the appellants were content to align themselves with the views of the Advocate General.
 It is unsatisfactory that there should continue to be room for doubt on this matter. So it may be helpful to summarise, quite briefly, three principles that should be followed when undertaking the exercise of determining whether, according to the rules that the 1998 Act lays down, a provision of an Act of the Scottish Parliament is outside competence.
 First, the question of competence must be determined in each case according to the particular rules that have been set out in sec 29 of, and schs 4 and 5 to, the 1998 Act. It is not for the courts to say whether legislation on any particular issue is better made by the Scottish Parliament or by the Parliament of the United Kingdom at Westminster ( Martin v Most , para 5). How that issue is to be dealt with has been addressed and determined by the UK Parliament. As Lord Walker observed in Martin v Most (para 44) its task was to define the legislative competence of the Scottish Parliament, while itself continuing as the sovereign legislature of the United Kingdom. The statutory language was informed by principles that were applied to resolve questions that had arisen in federal systems, where the powers of various legislatures tend to overlap (see Martin v Most , paras 11-15). But the intention was that it was to the 1998 Act itself, not to decisions as to how the problem was handled in other jurisdictions, that one should look for guidance. So it is to the rules that the 1998 Act lays down that the court must address its attention, bearing in mind that a provision may have a devolved purpose and yet be outside competence because it contravenes one of the rules. As Lord Atkin said in Gallagher v Lynn (p 870) an Act may have a perfectly lawful object but may seek to achieve that object by invalid methods.
 Second, those rules must be interpreted in the same way as any other rules that are found in a UK statute. The system that those rules laid down must, of course, be taken to have been intended to create a system for the exercise of legislative power by the Scottish Parliament that was coherent, stable and workable. This is a factor that it is proper to have in mind. But it is not a principle of construction that is peculiar to the 1998 Act. It is a factor that is common to any other statute that has been enacted by the legislature, whether at Westminster or at Holyrood. The best way of ensuring that a coherent, stable and workable outcome is achieved is to adopt an approach to the meaning of a statute that is constant and predictable. This will be achieved if the legislation is construed according to the ordinary meaning of the words used.
 Third, the description of the Act as a constitutional statute cannot be taken, in itself, to be a guide to its interpretation. The statute must be interpreted like any other statute. But the purpose of the Act has informed the statutory language. Its concern must be taken to have been that the Scottish Parliament should be able to legislate effectively about matters that were intended to be devolved to it, while ensuring that there were adequate safeguards for those matters that were intended to be reserved. That purpose provides the context for any discussion about legislative competence. So it is proper to have regard to the purpose if help is needed as to what the words actually mean. The fact that sec 29 provides a mechanism for determining whether a provision of an Act of the Scottish Parliament is outside, rather than inside, competence does not create a presumption in favour of competence. But it helps to show that one of the purposes of the 1998 Act was to enable the Parliament to make such laws within the powers given to it by sec 28 as it thought fit. It was intended, within carefully defined limits, to be a generous settlement of legislative authority.
The Scotland Act 2016 s.1; s.2
1 Permanence of the Scottish Parliament and Scottish Government
In the Scotland Act 1998 after Part 2 (the Scottish Administration) insert-
"PART 2A Permanence of the Scottish Parliament and Scottish Government
63A Permanence of the Scottish Parliament and Scottish Government
(1) The Scottish Parliament and the Scottish Government are a permanent part of the United Kingdom's constitutional arrangements.
(2) The purpose of this section is, with due regard to the other provisions of this Act, to signify the commitment of the Parliament and Government of the United Kingdom to the Scottish Parliament and the Scottish Government.
(3) In view of that commitment it is declared that the Scottish Parliament and the Scottish Government are not to be abolished except on the basis of a decision of the people of Scotland voting in a referendum."
2 The Sewel convention
In section 28 of the Scotland Act 1998 (Acts of the Scottish Parliament) at the end add-
"(8) But it is recognised that the Parliament of the United Kingdom will not normally legislate with regard to devolved matters without the consent of the Scottish Parliament."