Johnson’s UK Internal Market Bill is crucial not just because of proposals to break international law on Irish border. Also for its impact on devolution & governance of entire UK.

So: another step-by-step guide to key issues arising from Johnson's plans.

Voila:

1) Regulation of internal UK trade wasn’t much of a problem until Brexit. When UK joined EU, there was no devolution. When devolution happened, EU rules helped structure operation of UK market. Only a few issues ever bubbled up as points of tension, eg university tuition fees

2) But Brexit now makes it important to decide how regulatory differences across UK will impact on trade in goods and services. If Scotland has different rules on X or Y or Z, how far should those different rules prevent English goods / services being sold / provided in Scotland?

3) Trade law offers “toolkit” of principles to help decide how far regulatory differences should be allowed to disrupt trade. Most important is mutual recognition: if X is lawful in Territory A, then X can also be provided in Territory B, even if latter has different rules

4) MR is very effective trade tool (+ easy to manage, since no need for everyone to have same rules). But means Territory B must live with practical consequences of other countries picking different/lower rules. Might limit Territory B’s ability to enforce own social preferences

5) so many systems that rely on MR (like EU) incorporate safeguards into its application, eg wide range of justifications, so that Territory B can enforce its better / higher standards against incoming goods / services, eg to protect health / environment / consumers / workers

6) moreover, important that trade law tools take into account unique features of each internal market. In UK, that means the complete dominance of England over other parts of UK, not only in terms of population and economy, but also as regards political and constitutional power.

7) So UK “toolkit” needs to incorporate effective safeguards for devolved countries: able to make different choices without either London being able to overrule them at will; or English goods/services simply flooding local market & rendering devolved choices redundant in practice

8) yet that's precisely the internal market model Johnson has proposed in Bill: contains strong principles such as mutual recognition, applying across large sectors of economy, with only limited opportunities for devolved institutions to enforce own laws against English imports

9) which explains why Scotland & Wales are so angry: devolution looks OK on paper, but in practice, UKIM rules have potential to discourage regulatory innovation and limit capacity of devolved countries to pursue different economic or social choices from those made in London

10) important to stress: this isn’t directly about Scottish (or Welsh) independence - even if anger and resentment can obviously / understandably fuel calls for leaving UK. This is about respecting existing devolution settlements even within context of continuing UK membership...

11) how would I improve Bill? By recognising that real problem with UK internal market is not Scotland / Wales wanting to do things differently. It's the fact that, without proper constraints, these proposals will magnify England’s economic & constitutional dominance yet further

12) Eg much wider system of justifications, allowing Scotland & Wales to refuse mutual recognition for sake of broad public interest objectives. Eg proper system of pre-legislative dialogue between equals, allowing potential trade problems to be identified & resolved in advance

13) So while Bill is very important for Northern Ireland, EU-UK relations, rule of law, UK reputation etc… it is also very important for the entire constitutional management of the UK itself and especially for respecting devolution in Scotland and Wales.