"….Devolution of legislative competence to the Scottish Parliament does not affect the ability of Westminster to legislate for Scotland even in relation to devolved matters. …..we envisage there could be instances where it would be more convenient for legislation on devolved matters to be passed by the United Kingdom Parliament. However….we would expect a convention to be established that Westminster would not normally legislate with regard to devolved matters in Scotland without the consent of the Scottish Parliament." [ Emphasis added]
So was born the Convention which bore his name. It was quickly translated into "Devolution Guidance Note 10 - Post-devolution primary legislation affecting Scotland" (DGN 10). It has operated effectively throughout the years, although it is now known less colloquially as a Legislative Consent Memorandum and a Legislative Consent Motion. The procedures in Scotland are set out in Chapter 9B of the Standing Orders of the Scottish Parliament.
The Convention requires the UK Government to advise the Scottish Government if they intend to make policy proposals or legislate in a way which might affect devolved matters. The Scottish Government then draft a Memorandum setting out the nature of the proposals, and attach a motion asking the Scottish Parliament to agree the motion as explained in the Memorandum. A debate follows in the Scottish Parliament, after consideration and preparation of a report by a relevant Parliamentary Committee. Since this is a Convention, there is no legal sanction should the Scottish Parliament refuse to give their consent but the political fall out would be considerable. So far this has not happened.
The words of the Convention were enacted into statute as Section 2 of the Scotland Act 2016. While some thought this gave it greater effect, the Supreme Court, in Jan 2017, in their decision in the Article 50 case of Miller v the Secretary of State for Exiting the EU unanimously decided that enacting the particular words of the Convention into the Scotland Act 2016 did not lift its status above the weight given to a political Convention albeit an important one.
That being the case, the courts would not comment further. It did not give the Scottish Government any enforceable rights against the UK Government to be consulted and give consent in matters where the Convention applied.
So where does the Brexit angle come in? The UK Government advised the Scottish Government that an LCM was required for certain aspects of the European Union (Withdrawal) Bill. The Scottish Government produced a Memorandum in September 2017, but refused to put forward a motion on the basis they could not agree to the wording and terms of the Bill or recommend the Scottish Parliament consent to the Bill in its current form. They are looking for agreement that matters currently within the competence of the EU but which are related to devolved matters should come directly to Holyrood and not to Westminster. This is not what the Bill is designed to do.
It may be possible to reach agreement before Brexit as to some matters which can be transferred to Holyrood sooner rather than later but it remains to be seen whether that will satisfy the Scottish Government. The UK Government have identified 111 areas where EU competences intersect with devolved matters so there is wide scope for discussion and also for a failure to reach consensus.
We may therefore be heading for the first instance of no consent being given by the Scottish Parliament in a situation where the Convention would apply. The UK Government are legally entitled to proceed without Holyrood's consent to the Bill. However we may see some detailed legal justification from Whitehall as to what they think "normally" means in this kind of situation. The Convention may be about to reach another stage in it's constitutional development.