The implied odds of this happening are about 42%. In other words it is odds on that some thing/fudge/glitch will extend the UK's membership past that date. I don't get it - I would have thought this a 95% plus job that the UK will be out, not odds against.
The rules state: "For the purposes of this market leaving the EU is defined as the date when the treaties of the EU cease to apply to the UK. Examples of when this might occur include, but are not limited, to: the date specified in a withdrawal agreement between the UK and the EU; the end of the two year negotiating period (29/03/2019) as set out by Article 50 of the Lisbon Treaty (or any extension to this time period); or the date of the repeal of the 1972 European Communities Act. If more than one of these events were to occur, this market will be settled on the first of these events to occur. In the case of the two year time period in Article 50 being extended, via a unanimous vote by all EU Member States, we will settle this market on the extended date. This market will settle when the UK leaves the EU even if parts of the UK (e.g. Scotland, Northern Ireland) leave the UK or receive special status within the EU. "
So the little details in the rules favour being out by the deadline. Even an extension to the A50 deadline requires ALL member states to agree afaik.
You're assuming the Article 50 can't be withdrawn.
http://www.scottishlegal.com/2018/01/03/court-session-gives-unilateral-brexit-withdrawal-case-go-ahead/ The Court of Session has confirmed legal action can go ahead determining whether the UK can unilaterally halt the Brexit process if voters deem the final deal unacceptable.
If this goes through it will be up to the ECJ to decide.
You're assuming the Article 50 can't be withdrawn.http://www.scottishlegal.com/2018/01/03/court-session-gives-unilateral-brexit-withdrawal-case-go-ahead/The Court of Session has confirmed legal action can go ahead determining whether the UK can unila