The controlling BREXIT legislation is European Union (Withdrawal) Act 2018.

horshit: "Johnson's promises to find a way out of the backstop mechanism for Northern Ireland, the main sticking point." HoC forgot about breaking this law.
See
Main powers in connection with withdrawal 9. Implementing the withdrawal agreement;
Devolution 10. Continuation of North-South co-operation and the prevention of new border arrangements;
Parliamentary approval of outcome of EU negotiations 13.Parliamentary approval of the outcome of negotiations with the EU

horshit: "unprecedented constitutional crisis if he tried to defy the law passed last week and not seek a Brexit extension." HoC forgot about breaking this law.
See
SCHEDULE 7, Part 2, Scrutiny of other powers under Act. ¶14, Power to amend the UK [!] definition of TEU "exit day"; European Union (Withdrawal) Act 2019 regulating "exit day" 29 Mar => 12 Apr => 22 May => 30 June => 31 Oct

horshit: "The purpose of the Bill is simple: to ensure that the United Kingdom does not leave the European Union on 31 October without an agreement." Actual non sequitur.
See European Union (Withdrawal) (No. 6) Bill (HC Bill 433), "exit day"
Form letter set out in the Schedule to this Act to obtain extension

...I am writing therefore to inform the European Council that the United Kingdom is seeking a further extension to the period provided under Article 50(3) of the Treaty on European Union, including as applied by Article 106a of the Euratom Treaty...

I'm sure, BoJo could not say, "We don't give a damn," any cruder.

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