imagine the date is 19 October.I'm not sure that's clear. I see nothing to stop him taking a break and appointing a deputy PM in his short absence, able to request the extension. Then no law is broken.
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Bojo comes back from Brussels without a deal and goes on TV blaming the Commision, the ROI, Macron, Merkel etc.
In the chaos that follows, Court case, confidence vote etc, the UK can still hit the deadline without asking the EU for an extension of Article 50.