Many of the peeps who follow this account are far more accomplished in Public International Law than I, so this mini-thread is mostly for the for the record.

Legislation by Westminster cannot “eliminate the legal force of parts of the withdrawal agreement”, in two ways: 1/ https://twitter.com/pmdfoster/status/1302702474957070336
1. Axiomatic and elementary to the point of banality: in international law, a treaty does not lose its "legal force", in whole or in part, by the actions of one party alone.

Well, OK, not nuanced enough: a party can terminate a treaty in accordance with its term. Or it can be 2/
in fundamental breach and bring the treaty to that end. But not through selective application of domestic legislation. The treaty, all of it, remains in force. Domestic measures to the contrary would be in violation of it terms, however they are characterised.

2. The UK is a 3/
dualist system.

It means that unless a treaty is directly and wholly incorporated by reference in UK law, the treaty itself does not legal force at law domestically. In this sense, domestic legislation cannot affect the "legal status" of a treaty because it has none.

4/
Many will read this tweet as heartwarming; I read it as deeply alarming.

Only "a lot of" Whitehall? And only instrumentally?

The voice of Daniel Patrick Moynihan rings in my ears: you don't do it because *it is the law*, not because it's not helpful. 5/

https://twitter.com/pmdfoster/status/1302704329040842753
The rule of law has its roots in interest, but its operation must be principled and not instrumental. *All* of Whitehall should be horrified because of the *principle* at stake and not just because of potential impact on Sino-UK relations. 7/ https://twitter.com/GenevaTradeLaw/status/1300804732856958976
This might be a problem of transposition, but either the Protocol has legal force in international law, or it does not. If it does, UK legislation may not "supersede" its terms or narrow them unilaterally. The correct word here is "violate". 8/ https://twitter.com/pmdfoster/status/1302708220990029825
One final word on the effect of this "gambit" on future UK trade relations.

It's difficult to make predictions, especially about the future. What's not difficult to predict is state risk assessment in other capitals in respect of future UK conduct. 9/ https://twitter.com/pmdfoster/status/1302709264008523778
Every responsible trade department will add a section to their cabinet memoranda on "The NI Gambit", comprising at least two factors:

1. NI and the Protocol and the UK WA are sui generis and unlikely to replicate themselves; and
2. In respect of its closest economic partner 10/
the UK demonstrated an alarming capacity to violate a newly negotiated and ratified treaty because "fall-back options"; caveat emptor.

This does not mean no future FTAs; it does mean more difficult negotiations to address the increased risk of doing business with the UK. 11/
One final note.

It's always hard to gauge "good faith" in *negotiations*; in the long run interest will prevail over perceptions of reputation. As for good faith in *ongoing relations*, doing business with the UK will now involve a risk premium. /fin https://twitter.com/pmdfoster/status/1302711905816121349
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