Interesting analysis.
1 and 2: My point remains that a PM should not be FORCED to sign a letter against his will without a Super Majority vote of its Parliament. In my opinion of course it’s a personal opinion of principle not a technical legal one
3: If the other nations accept/approve a request that is knowingly signed under duress. Even if legally permissible would raise serious moral and ethical questions. Agree?
4: I believe the proverbial ball is in the court of each EU member who will knowingly vote to approve an unsigned or a signed under duress request of another member.
1 & 2 -> it was a cross-party law passed. That’s the system they have. Boris could have resigned or refused. Instead he played games
3. Then the other countries would be acknowledging that the British PM is no longer in charge and the UK does not have a functioning government
4. As I pointed out - the response is “You forgot to sign this”