This paper (Stanley Brodie QC, 3rd June 2019) argues that we left the EU at 23:00 on 29th March 2019:
(5.1) ...The conclusion, I would suggest, is that the Agreement used and implemented by the Prime Minister, Mr Barnier and President Tusk was unlawful and ultra vires Article 50.
The first extension proposal, on 14th March to extend to 30th June, was lawful but was rejected by the EU. Subsequent shenanigans, which leave us with 31st October as the latest deadline for the apparat to ignore, were unlawful and skullduggerous:
(5.4) ...the civil servants responsible for briefing parliament to enable an informed debate to take place, themselves were misleading it. The alteration of the text of Article 50, and of the proviso to paragraph 3, must have been deliberate.
The beneficiary of this misconduct was the Prime Minister, who could and did arrange for extensions of time without hindrance.
Thus we left on 29th March absent any lawful alternative. An interesting case, though I suspect that lawfulness is not a consideration.
