Useful moment to recall what happens at end of transition period (1 January 2021) if, as Johnson seems determined, there is no significant agreement in place between EU & UK, so latter suddenly & comprehensively discovers what it really means to become a 3rd country. Few points:

1) Like it or not, UK will remain bound by international obligations under Withdrawal Agreement, many of whose provisions will only then become fully effective, e.g. those on future protection of citizens’ rights; e.g. Johnson's new regime governing Irish border.

2) Irish border regime is particularly crucial. Even if it works as planned = serious problems for Northern Ireland. If UK deliberately scuppers its operation, consequences could be catastrophic – for international reputation, other proposed deals, above all peace and stability.

3) Otherwise, UK relations with EU & every other international actor will be governed by whatever treaties exist/are created anew under international law. Attention tends to focus on trade, e.g. minimalist WTO terms for EU + everyone else where no “continuity agreement” is ready

4) But it's not just trade: every other field of policy & cooperation is potentially affected too, e.g. combating organised crime, security & counterterrorism, transport, science etc. Even UK admits huge work still to do just to reconstruct existing cross-border networks & ties.

5) Closer to home: we will discover whether the 11 months of extra time afforded by transition period were really enough to allow all relevant public & private actors across entire UK society & economy to complete their preparations for the full internal consequences of Brexit.

6) E.g. will necessary legislation be in place for up-and-functioning regimes on agriculture & fisheries? Will domestic replacements, needed to duplicate all EU agencies, be fully operational? Will London have settled terms of UK’s own internal market with Edinburgh and Cardiff?

7) And all that is against background of an unprecedented national, European and global health & economic crisis - that has already wrought / will continue to inflict abject havoc upon plans, timescales & preparations that were already seriously unrealistic.

So: UK Government's breezy confidence and optimism looks more like gross arrogance and wilful negligence. As I've said before: Johnson's planned No Deal Brexit on 1 January 2021, amid terrible health and economic problems, will = an entirely deliberate and avoidable extra crisis.