Any general election, and any change to the EU treaties that cedes further power to the EU (as the law currently stands I think).
I've banged on a lot about Remain, but I don't by any means dismiss these concerns. They are perfectly sensible and many people share them.
I hope I haven't dismissed anyone out of hand (well, except for Tak3n - but he was really pushing his luck).
What I do disagree with is the claim (made by both sides) that this is a once-in-a-lifetime thing, and that voting to leave now is without bad economic and political consequences in the short to medium term. And it is the risk of immediate financial and political fallout that most worries me.
As I've said above, we can trigger exit any general election we want to by voting in a party that has Leave in its manifesto. In addition, there are likely to be votes on any further cession of power to the EU. It's not a once in a lifetime opportunity to leave. It is a once in a lifetime opportunity to Remain on anything like our current terms.
Of course you don't have to vote to Remain. Any moral approbation I have is for the self-serving power-grabbers who claim without serious basis that leaving now is the only road to Oz regardless of the consequences. And given who they are and the company they keep, I'm rather worried about the political landscape of the UK should Leave win today.
Best wishes, and vote the way you want to.